Reddit is a platform for communities. Some communities, across all spectrums of topics, find reasons to create a somewhat exclusive environment. They are not required to make space for all views, and that lack of forced-openness is not the same as censorship.
/r/conservative does the exact same thing, why the handwringing about that sub in particular?
I feel it's important to note that a similar restriction focused on any other race, even other minority races, would probably be banned within a week of creation.
there is a disturbing pattern the administrators have of proclaiming their love for freedom of speech in a post, receiving huge backlash, then going on a banhammer rampage. it's happened at least four times /in my memory/, and probably more throughout the site's entire history.