Upvotes do not suppress the readability of comments. That workarounds exist is beyond the point.
Supposing we take your argument seriously though, comments past the page fold which also have their contrast lowered to the point of illegibility are certainly censored even moreso.
Incidentally, I do think the way the comment fading works is pointedly user-hating and dumb (it's traditionally dumb, though!), but it's not really censorship. More generally, since we're talking about taking things seriously, framing forum irritants as some sort of oppression is a solid way to ensure few people take you seriously.