This made me reflect on online interactions.

Agreeable comments will draw comparatively fewer replies, while disagreeable ones achieve the opposite.

But this then results in a "false experience" for the individual, where unlike in real life, the bad exchanges do not end up outweighed by the good ones, as you simply don't go on to have those. You just upvote and move on (often to avoid redundancy).

Maybe if the two were tied together (voting either up / down & sending a reply), communities would work healthier? I don't know. Not like it's easy to have this tried out.

I could definitely see challenges to this though, the aforementioned redundancy being one. I have some countermeasure ideas, but then I wonder if that would make the UX complicated enough to drive people away instead, which is a lose-lose.