Not everyone enjoys the literally daily deluge of messages advocating for and defending the continued practice of literal genocide - so long as it is done by the "correct" side of whatever conflict - e.g. the constant (and oftentimes graphical) depictions of beheading landlords. However, others very much do enjoy that - so how do we all get along?
Unlike X (formerly Twitter), under Musk's "benevolent" authoritarian reign, or Reddit under Huffman's, the Fediverse is not a singular "place". We are more like an assortment of loose pirate & free-trader ships, passing in the night, and conveying messages from ship to ship. This means that each instance gets to choose what is deemed "acceptable content" - and in a global context, there are bound to be disagreements (some will say that Donald Trump is the only politician who ever speaks the truth, others the opposite, and still others are tired of it, or of all USA politics that worms its way into entirely unrelated communities).
Below, I will mention some coping strategies, assuming that you are using the webserver UI of a Lemmy instance, although many of the strategies surely apply, with minor tweaks to find what to click, in Mastodon, Mbin, PieFed, Sublinks, etc., and in your app of choice (but also note: if at worst you need to modify your account settings using the web UI, it should also affect your experience in the app? ymmv there though). Also, I presume that you've already taken a breather, gone outside to touch grass, etc., and here I'm focusing on how to take action to literally change your experience on the Fediverse, forever (for that account). Whereas to people who want to see every comment from every person regardless of content or source, this post is not for you, just move along:-). Finally, note that I am starting from the most strict set of solutions - not that I am advocating for those in particular, but that's just how the Fediverse works, so it is good to know about the choice even if retroactively after you have already made it.
Picking your instance
Some instances are known to be more closed-off than others. See also Lemmy Explorer. e.g. Lemm.ee and Lemmy.zip are among the most neutral & open, exposing its users to all political content everywhere, while lemmy.cafe is literally the only instance that I've ever heard of that has defederated from all of the Big Three leftist extremist instances.
A point related to this is that unlike such general-purpose instances as mentioned above, if you are exclusively interested in just one topic - e.g. for science, then mander.xyz; or for programming, then programming.dev, etc. - then you can just always browse by "Local" rather than "All", and you will avoid all of the politics, memes, and general-purpose discussion communities on the Fediverse. The down-side is that you will miss the vast majority of what the Fediverse has to offer... but maybe you can tolerate it in small doses, and perhaps being able to switch it off & on from the same account is attractive to you (otherwise: make an alt account on another, general-purpose instance?). If this works for you then great, but I will offer many other tips in case it does not:-).
Picking your communities
Similar to the above, if you restrict yourself to viewing content exclusively from your previously "Subscribed" list, then you can avoid most content that you do not want to see. This is of course a very imperfect solution, for most people, b/c how do you discover new content, and entirely new communities, that way? Also, extremism tends to find its way (as posts or comments) into seemingly unrelated communities (such as communities labelled only as "memes"), so it is not as firm a solution as a user or instance block would be. But perhaps it will be sufficient for you, so I wanted to at least mention that it is a possibility.
NSFW
Quick side-note about this: many instances outright block NSFW content by default, while others allow it but require it to be appropriately labelled. Look in your account Settings to fine-tune this further if you want - e.g. in Lemmy there are 2 relevant ones: "Show NSFW content" and "Blur NSFW content" (the default setting for each depending on what your chosen instance has decided for new accounts), and then there are others that affect media content in general such as "Auto expand media".
The point is, you have a LOT of control over this aspect, as people tend to be fairly good about labeling this content - i.e. whenever my setting is off, I have literally never seen a stray NSFW post in the past year since I came to Kbin, then bounced around across several Lemmy instances. This aspect of the Fediverse is tightly regulated and thus very friendly to people on both sides who respectively want or don't want to see it.
Blocking instances
Unfortunately, people refuse to label "extremist" content in the same manner as NSFW. This includes the extreme Right - which mostly has moved off of the Fediverse entirely these days - and also the extreme Left, who despite calling themselves "leftists" seem entirely okay with fascism/authoritarianism, or conversely democracy and capitalism, so long as it is done by their preferred vendor of choice (top culprits include Russia, China, North Korea, etc.), but simultaneously tends to be vehemently against steps taken by the Western world to become more socialist/communist, citing how anything short of a violent upheaval of entire societies "does not go far enough". Of course, this is my own POV, feel free to make your own:-).
Anyway, (much like the situation with NSFW) you should feel free to do whatever you want, so long as I also am free to do as *I* please as well - which includes not having to "enjoy" such content appearing in my feed on a daily basis. The trouble is that unlike the situation with NSFW, extremists tend to resist all efforts to either label themselves, or to be labelled by others. Therefore, I am going to offer my own list, which will necessarily be biased and imperfect. But my hope is that one day we as a community can get together and collectively decide "(value judgements aside) this is an instance that advocates for extremist policies, which many moderates may want to know about", with the exact wording ideally having been offered by the very community that it pertains to. A tiny bit of consideration would go a long way... however, Lemmy is still in beta, and this aspect lags greatly behind that of others.
The goal then would be to, like NSFW, offer you a choice to not see such content, if you so desired. This will cause (a) those communities to not show up in your All feed, and (b) though you can still see individual user comments, you will no longer receive Notifications from users on these instances - you can reply to them and they can reply to you, just without a Notification sent to you each time (which if you have ever had experience accidentally commenting in certain communities, you will realize is a good thing, since consent does not always matter to some people who continue to dunk on what you thought was an innocuous comment for weeks and weeks afterwards). Note that they can still down-vote your content though, thereby influencing the degree to which it shows up for other people (and yes, brigading is both popular and allowed), when sorting by e.g. Hot - the only way to fully prevent that would be full defederation, mentioned below.
My list: 99.99999% of the time when I see the most batshit insane comment from someone - e.g. "where is your proof that the sun rises each day?" or "you are so stoopid, don't you know that the answer to the question of what does 1+1 equal depends on various factors?" - they are from the same Big Three instances: lemmygrad.ml, hexbear.net, lemmy.ml, and lately I am starting to see it from midwest.social (though the latter with the heavy distinction that many of its individual users simply see the word "midwest" and don't realize what they have gotten themselves into; and somewhat similarly for lemmy.ml but I no longer care anymore b/c it's just too much from them, constantly, so I am willing to lose all positive benefits from associating with them if it means that the negatives can also finally be stopped). Mind you, even if you do not take issue with the content from such sources, the manner of presentation being so extremely often highly hostile can be quite off-putting to some of us - so again, if you don't want to block them, then don't, whereas this message is intended to let people know that they don't have to put up with that.
If you go into your Settings (not Profile), in the Blocks tab, scroll waaaay down (if like me you've already blocked several users & communities), then you can add to your Blocked instances list. Occasionally I also find it helpful to block instances such as feddit.org that otherwise fills my feed with posts not in English, and kbin.social that unfortunately went defunct but before it did it went entirely unmoderated for months and allowed a large number of advertisements to flood the entire Fediverse.
Note that most instances will block many of these for you, so you may want to check there first (scroll all the way down and click Instances, e.g. lemmy.world's list) - e.g. lemmy.world blocks lemmygrad.ml and hexbear.net, but not lemmy.ml. Unlike a user block, an instance-wide block (called "defederation") prevents any and all comments from those users from showing up on any post; this is widely considered a "last resort" measure when all other attempts at not even friendliness but peaceful coexistence has failed. But if you are on an instance that has not blocked one that you want blocked, I wanted you to know that there is hope, you don't have to move, you can block them yourself, as a user - again they can still comment on your content, and mostly anonymously vote on it, etc., but it does mitigate the level of interaction greatly.
Block individual communities and/or users
This is much easier to do: simply visit each community or user in question, and click the giant Block button near the top of the respective community/user page. You won't see their comments anymore, and I'm not certain but I think they can't downvote you either? If you ever want to see their content, either create an alternate account that does not block them, or visit an instance where you are not logged into an account - e.g. the rainbow network Fediverse icon, next to the Share button, may work, if the content originates from a different instance. New communities and user accounts are constantly being created though, so this process will never fully end, if you want to scroll by All rather than Subscribed.
You can block a variety of things this way - communities for various sports, or individual places. !196@lemmy.blahaj.zone is a very common one to block, b/c it has a particular brand of humor that can be offensive to some even as it is attractive to others.
Notably, you may want to preferentially block communities and/or users, but save blocking instances for the most extreme cases where it will cut you off from a lot of content. However, now you know the most important thing: that the choice is yours to make:-D.
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Finally, this post could be improved upon in a number of ways. I do not intend this as the last word on this subject, but rather as a first draft to help get us started!:-) Feel free to ~~plagiarize~~ borrow any of this as you take the matter forward, to improve conditions for us all.
Hey I have an idea, let's put him in charge of... "Technology"?