Downvotes were often turned against trans folk on reddit simply because they're openly trans. I have no desire to see that repeated here, and so I disabled them when we were setting up the instance.
Given that lemmy still has plenty of transphobes, it's unlikely we'll change it any time soon. Ideally, it would be a per user setting that allows the admins to set the default settings for new users, but that's not functionality that exists at this time.