It is difficult for me to ascertain when the person I am communicating is using a logical fallacy to trick me into believing him or doubting my judgement, even when I realise it hours after the argument.
I have seen countless arguments in Reddit threads and I couldn't figure out who was in the right or wrong unless I looked at the upvote counts. Even if the person is uttering a blatant lie, they somehow make it sound in a way that is completely believable to me. If it weren't for those people that could exactly point out the irrationality behind these arguments, my mind would have been lobotomised long ago.
I do want to learn these critical thinking skills but I don't know where to begin from. I could have all these tips and strategies memorised in theory, but they would be essentially useless if I am not able to think properly or remember them at the heat of the moment.
There could be many situations I could be unprepared for, like when the other person brings up a fact or statistic to support their claim and I have no way to verify it at the moment, or when someone I know personally to be wise or well-informed bring up about such fallacies, perhaps about a topic they are not well-versed with or misinformed of by some other unreliable source, and I don't know whether to believe them or myself.
Could someone help me in this? I find this skill of distinguishing fallacies from facts to be an extremely important thing to have in this age of misinformation and would really wish to learn it well if possible. Maybe I could take inspiration from how you came about learning these critical thinking skills by your own.
Edit: I do not blindly trust the upvote count in a comment thread to determine who is right or wrong. It just helps me inform that the original opinion is not inherently acceptable by everyone. It is up to me decide who is actually correct or not, which I can do at my leisure unlike in a live conversation with someone where I don't get the time to think rationally about what the other person is saying.
The trouble with 'Slippery Slope' and 'No True Scotsman' is that they themselves are not fallacies. Invoking them without proper justification is the fallacy. The same sort of thing happens all the time with 'Appeal to Authority', you can probably trust a scientific consensus about a subject in which they are all experts, but you probably shouldn't trust an individual expert on a topic for which they are not recognized as an expert.
For an example of Slippery Slope: Fascists will absolutely try to demonize the most available target, and then because they always need an out-group, they continue cutting at what they consider the 'degenerates' of society until they are all that remain. (And then they find some new definition of degenerate)
"No True Scotsman" is valid in that there is at some point by definition after which you are no longer talking about something. "No true vegetarian eats meat" is valid, as this is definitional. "No true member of Vegetarians United eats meat" lacks proper justification, and refers to an organization, not a proper definition. This gets really messy when people conflate what group people are in with what they 'are' or what makes them a good example of a group. Especially when religion is involved.
That in itself is the ad hominem fallacy: you need to judge the claim based on its merits, not the merits of the person making the claim.
For example when David Suzuki talks about climate change and people say "well he's just a biologist, he's not qualified!" That may be true but it doesn't invalidate his statements.
No true Scotsman is a fallacy, more specifically ad hoc while defending a generalisation about a group defined by another criterion. Easier shown with an example:
If we accept the definition of vegetarian that you implied (someone who doesn't eat meat), "not eating cheese" is at most a generalisation. As such, when Alice says "Those who eat cheese are not true vegetarians", she is incurring in the fallacy.
The slippery slope is an interesting case, because it's both a fallacy and a social phenomenon. And evoking the social phenomenon doesn't automatically mean that you're using the fallacy.
As a fallacy, it's failure to acknowledge that the confidence in the conclusion is smaller than the confidence in the premises - so if you're chaining lots of premises, your trust in the conclusion will degrade to nothing. Here's a simple example of that:
So if A happens, what's the likelihood of G also happening? It is not 90%, but (90%)⁶ = 53%. Even with rather good confidence in the premises, the conclusion is a coin flip. (Incidentally, a similar reasoning can be used to back up Ockham's Razor.)
As a social phenomenon, however, the slippery slope is simply an observed pattern: if a group, entity or individual does something, it's/they're likely to do something similar but not necessarily identical in the future. That covers your example with fascists.
The reason why appeal to authority is a fallacy (more specifically, a genetic fallacy) is because the truth value of a proposition does not depend on who proposes it. If an expert said that 2+2=5 (NB: natural numbers), it would be still false; and if the village idiot said that 2+2=4, it would be still true.
We can still use authority however, but that requires inductive reasoning (like the one I did for the slippery slope), that is considerably weaker than deductive reasoning. And it can be still contradicted if you manage to back up an opposing claim with either 1) deductive logic, or 2) inductive logic with more trustable premises.
I think part of it is they're logical fallacies. For instance, the scientific consensus on climate change is not technically proof of climate change; rather, it's all the observations, statistics, etc. that are the evidence for climate change. Thus, it is true that claiming an argument is true solely because of scientific consensus is indeed a logical fallacy, as logical fallacies are relating to, well, logic.
For all practical purposes, however, we live in a complex world with lots of uncertainty, and we can generally trust expert consensus if for no other reason than they're more likely to understand the facts of a certain technical matter better than us, and thus more likely to be able to ascertain the truth. And when discussing complex, technical concepts, I'm generally going to trust expert consensus so long as I am reasonably assured that they are indeed experts and that they have no systemic conflict of interest.