It'd be nice if we can all agree on that, but that's an inherent problem with an increasingly large community. I'm afraid we won't be able to get the "crowd" to agree to use the arrow properly. I don't know of any site that has been successful in that endeavor.

Say people view the up vote as a button to say, "Yay, this gives me a positive feeling!" If a snap makes you laugh, you agree with its point, or you think it's worth being seen for any other reason, you're going to hit the up vote. Of course, if there's another button simply pointing down, it's natural to use it for the opposite reason. If a snap isn't contributing value, makes you angry, and/or you disagree, your instinct is to use the negative button.

It's really just a matter of perception, and I think that could be changed by moving away from the up-arrow/down-arrow system.

Edit: I do like that the arrows aren't shown until you hover over the comment, though! It's a subtle way to encourage reading the comment and thinking about it before actually making a judgement.