When I think a opinion shows wisdom and insight into a matter I tend to upvote it. In some cases I'd also upvote if the person said something clever or funny.
I downvote if the person is attacking someone or a group of people in a disrespectful manner OR when a opinion is of no help whatsoever and is just basically the person wanting Xper points while doing minimal effort.
Some people do. Some people want to get their kicks off this site. It's just society at it's best. Upvoting an opinion is basically saying Hey this is a good answer, I like it. And Downvoting is saying, this comment was shit. And personally, I don't care but you get points for it so, It does something, I guess.
I tend to up vote most opinions on my posts. Unless the opinion is totally idiotic. If someone has taken the time to post an opinion on my question. Then I like to give them an Xper point just for the hell of it.
I upvote the ones I find funny or who make a good point. And I downvote the ones that I 100% disagree with. I try to avoid giving downvotes because I like to be a nice person haha And when I get more than 3 upvotes it makes me feel smart c: