The ability to up- and downvote posts and comments is useful but the score should not be displayed to the users and you shouldn’t be able to enable it even if you wanted to. This means both, posts made by you as well as by others.
Nobody wants to see their messages get downvoted. This is bad for our mental health as individuals but especially as a group. It’s like walking up to a person on the street, saying “I don’t like you” and then moving on. You’re free to not like (downvote) someone but they don’t need to hear it. If you really want them to know then write a message and explain yourself.
Upvotes on the other hand skews the reality and encourages groupthink. People say what is popular even if they don’t fully buy it themselves and conversely refrain from saying things they truly believe because they then dont get the upvotes and get downvoted instead.
Seeing the scores also primes the reader. When something is heavily upvoted for example you assume it to be true/good instead of using your own judgement to decide.
I cannot speak for others, but I’m focusing on downvotes because you talked about downvotes and mental health (I even quoted you).
I kinda, sorta, 50% agree with the part about “upvotes”: I get what you’re talking about but I don’t think the “like/dislike” system is the cause of “pack mentality” in social media. I rather believe it’s an effect of this human aspect and it shouldn’t be stigmatized, but used as a point of reflection about the environment in which we post our topics.
But I’m not a psychologist or an anthropologist, so I’m not gonna argue with that.