I think it's even worse: upvotes are upvotes, and the reason why someone clicked it varies. It could mean "I agree," "this was well stated and insightful" or even "I disagree and it's dumb and mean but so represents common sentiment that I think everyone should read this."

The symbol is a little triangle, and inherently says none of those things. People will click to mean whatever they mean.

Person feel obliged to register their opinion on some question. And upvoting appears the only acceptable way to do this (since "me too"-kind responses get downvoted quickly). So I think the ways to increase voting quality are: 1) allow to register user's agreement/disagreement with the post separately of the post itself (like another voting button), or 2) say in rules that you can't display your agreement or disagreement by upvoting. I think 2 is the best, since users will be forced to make sufficient contribution when they agree or disagree.