Downvotes are primary a tool to regulate how rewards are distributed from the rewards pool. I don't know of a single downvoter that uses his power because he wants to censor other opinions. If somebody wanted to use downvotes as a censorship tool, they had to assume that the audience of the "censored" person uses steemit.com or another frontend that hides downvoted posts.

This is not censorship, first because of what I described above and second it doesn't make the Information harder to access, if you have to click one button. Or do you also think marking posts as NSFW is censorship?

What steeminc does to @thedarkoverlord is indeed censorship, because you don't even get to know about the existence of a post made by this account, in contrary to hiding posts.

I can't write a more detailed answer, as I'm on my phone right now.

Edit: And just because it walks on two feet, like ducks do, it hasn't to be a duck