The number of people on this site who feel the need to defend it against any discussion of its population's racism is so fucking absurd honestly.
"It's overwhelmingly queer white people!"
"Tumblr isn't racist, it's just a few bad apples!"
"At least we're not Reddit!"
The cognitive dissonance is immense. These people live in a mental state where they can only justify inhabiting a "morally pure" platform - one that is largely free of bigotry and other "problematic" beliefs - but since this mindset should naturally rule out Tumblr altogether, they bury their heads in the sand and make up justifications that excuse its problems, so they don't have to actually hold themselves to this absurd and harmful belief. And any time they're forced to actually confront the existence of real problems, they bring in another social media site to act as a scapegoat: "well we might be bad, but THOSE guys are worse!"
I cannot stress enough that if you want to be a "moral" person, this attitude is completely self-defeating. Like, nobody is saying that you're a bad person for using a site where people are racist. They're saying people who use this site need to quit being racist. And framing the conversation as if it's about Guilt By Association is not only wrong, it is a tool that forcibly suppresses conversations about racism by making white people into innocent victims.
If you're having a hard time following, here's how it works:
OP mentions that Tumblr is full of racist white people. This is not a condemnation of white people who choose to use Tumblr, it is a condemnation of white people who choose to be racist.
White people see the above post, and feel guilty about the possibility that they may have done something racist, but also can't think of anything racist they may have done. But the guilt makes them feel like they must have done something wrong, if only by OP's standards, and therefore they conclude that they are being blamed for sharing a space with racist people.
Rather than acknowledge that their guilt is a product of their own mind, and has nothing to do with the OP's intentions, they treat the OP as the instigator and start harassing them with excuses for behavior that they weren't being blamed for in the first place.
It becomes impossible to have any discussion about racism because "innocent" white people cannot stop making the conversation about themselves for five goddamn minutes.
So yeah. Quit fucking doing this. Quit assuming every sweeping statement is about you, quit trying to establish Tumblr as a morally unimpeachable platform, and learn to process your guilt instead of trying to bully other people into absolving you.