I'd think so. More popular threads would 'cost' more to post in and there would then be less posters in it as a result. 'Brigading' would be difficult.

on the contrary, popular opinions would gather more karma, thus allowing them to share their ideas more often, unpopular opinions will quickly have their posting ability removed via downvotes. Soon enough only the prevailing popular opinion will be found

I had the same idea at first but I don't think it would work in practice

Hmmm, you're right. Perhaps a sliding scale then? The cost to up/downvote increases exponentially?