I think it keeps the people from saying what they want or how they want to say it. I saw an AskReddit post once that asked why do people on reddit sound like the same person. Well it was because in time, in order to keep or gain karma, everyone would eventually sound like the generic user.

I think the problem with modern reddit is that it does not show total upvotes but just shows net upvotes (iirc people also said that after that change things got worst on reddit), When i write a comment there is always doubt about if it’s worth my time, on reddit someone can write something unpopular and get downvoted and think it’s not worth it (you can mark comments as “controversial” but that is off by default iirc), on lemmy i can write it and still get a net negative of downvotes but if i see upvotes i get positive feedback that my efforts are at least appreciated and i am not wasting my time.

Trying to just prevent positive feedback is problematic, eventually the root of the problem is someone having a impulse control problem or a personality that scores high on the immoderation scale of the big five model and that could cause other problem in his life.

IMO you can do anything you like on lemmy as long as you link to good mental health or self improvement resources and maybe some scientific knowledge about the dangers or significant downsides of social media.