Why is it "fine" to tell people they can or cannot visit your blog because of their skin colour? It doesn't matter what the blog's content it, it's still wrong and moderately racist to tell white people they cannot visit your blog. And yes - it is possible to be racist to a white person, even though most people seem to believe that because white people are so "privileged" that it's impossible to be racist to them.
Like most people on tumblr want black people and/or other people of colour to be accepted and to not be given abuse, but they're just as bad as racist people if they're going to hate white people
