Indeed. Spam filters, porn filters, swearword filters... all of those have precedents (in mainstream, non-social/internet media) and are perfectly acceptable by most of society.

In addition, notice that even GMail doesn't actually filter spam. It just hides it - it's an assistant, not arbiter of what you should see. It's more than happy for you to adjust the filters (for yourself personally).

Edit: GMail also does prioritization as of recently - but again, the purpose of that is to help users not filter content. Again, those algorithms are also adjustable for each user separately, they just have some "smart" defaults.