Muting within a community mutes the post from everyone viewing posts in that community, not just the person doing the muting. So a community lets you setup a "safe space" to share information between people who share a common opinion about what sort of expression is ok and what sort isn't.
As far as the guy with the bag over his head, his post was extremely distasteful and got massively downvoted, but if you review his "introduceyourself" post, you will find he described his forthcoming posts as:
My sense of humor will not be censored. My opinion of worldwide topics will be heard. Truth will prevail. If you do not know how to take a joke, prepare to be offended rather often.
So I never thought for a minute he was serious about what he said. He's setting himself up as a shock jock and the bag is obviously part of his shtick, as he apparently uses it in all his posts. Nonetheless, it's not to my taste, no more than I enjoy listening to Howard Stern (sorry Stern fans, don't take it personally).
Well stated.