I'm aware I can say things that people don't like, yes, but in some cases it's more beneficial to have a respectful debate than to stay silent. If I'm not prepared to listen to opposing opinions then I'll be robbing myself of getting a deeper understanding.

So, why comment if an downvote is enough, as you say?

A downvote is second best to a comment explaining the reason behind the disagreement. A comment is better feedback than a vote because you can get a clearer understanding from a comment.