There are some rules and while it is extremely open and free there has been at least one case I'm aware of where someone's content was pulled down and censored because it was illegal. It involved child porn, so it is possible to censor people if they do something extremely horrible, you just need a super majority of the top 20 witnesses which I think is 17 out 20.

But.. For the most part the community polices itself, if people are doing wrong other people in the community will point it out or try to use flags if they can, so.. Generally you can do whatever you want for the most part as long as it's not extremely illegal! Though, just like in the real world if you go disrespecting certain people they might take issue with you, so.. You're much more likely to get some other general users trying to intervene as opposed to the top 20 witnesses or steemit inc.