Quoted from NJGecko:
The mod team has talked about this a few times. It was revamped a few months back and it's not thumbs up or down any more.
It's an agree or disagree. Not a down vote in a negative connotation at all. People disagree and that's all it's meant to signify.
When you hover over the buttons, you get pop up text that literally says "upvote" and "downvote" =P