[pvg]

But one person's tropes and memes are often somebody else's current belief/position

In a site with the ostensible goal of 'curious conversation', that's not really good enough - it's not the job of your potential interlocutors to figure out what sincere, reasoned beliefs and positions hide behind the throwaway trope line. If you want to have a conversation, it's on you to try to converse. There are lots of other places where the trope line is fine - from the group chat with friends or colleagues to twitter. But those places work in different ways.

What (in your opinion) is the purpose of the down-vote button?

It's a way to say 'this comment is misranked'. There are lots of reasons to feel a comment is misranked - including simple disagreement.