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.
My brain on a Monday in a crap mood driving on the highway: that jerk that just cut me off has ruined my entire day.
My brain on Friday after good sleep and a relaxing morning: heh look at the guy, he's definitely in a hurry. Hope he gets where he's going, back to my jams!
I try to train myself to remember to be Friday brain, but sometimes Monday brain comes out and I'm in a funk that makes me forget I actually have a choice about NOT reacting a specific way. I like to think I'm getting better at consistently not sweating the small stuff and just letting those instances go without giving them an appreciable amount of mental space better suited to relaxing and listening to good music.