As I said, quietly writing in my notepad, I was approached by a white male attendee. He did not ask if it was a good time to approach me; he did not seem to care that I was obviously working. He just sat next to me and said, "oh good, now I can talk to you. I have a question." The man did not wait for my consent to the conversation. He just dove in.
He described a few of the political activism groups he's involved in, mostly around environmentalism. ...And he was sure that, just like every other event he had attended, it would be populated exclusively with white people. He would love to see more people of color at these events, he said, but they were nowhere to be found. "Why," he asked me in conclusion, "don't people of color care more about important political issues?"
Many white men see a political landscape dominated by white men and think it is that way because white men are just more politically minded. They think that the absence of women and people of color from powerful rooms is due to self-selection.
They do not question how unwelcoming the room they have built might be. They do not question whether or not the discussions they are having in that room are inclusive and generate productive discussions for women and people of color. They don't ask if there are other, equally important conversations happening in other rooms. And they don't even bother to ask if anyone unlocked the door.
They look at the room and say that women and people of color aren't in it because women and people of color aren't interested. Then they cite this supposed disinterest as proof that women and people of color are too unqualified to even be invited in."
Chapter 6- Mediocre, Ijeoma Oluo
For a Tumblr-specific example, this is why if you don't "see" Black people in your fandom spaces, there's a reason for that. It usually means the space is unwelcome at best, actively hostile at worst. You just don't perceive it bc it doesn't directly affect your entertainment.