Yeah... There are people who find 4chan scary, but I rather sit with those predictable as$holes than the deep space tumblr people. Holy crap was I blissfully unaware, and I've been on tumblr for 6 years. I have no idea how i never encountered it until now.
I've been on Tumblr for quite a long time, and a good chunk of my blogroll consists of Tumblr activists in varied area (feminism, trans rights, queers, asexuals, POC rights, disabled people) and while some can be quite radical, not once have I found them to be scary or acting like assholes. On the contrary, they're insightful and intelligent people that helped me shape my views on the world, and made me become way more radical and politically/socially aware that I was before.
But the activist sphere can also contain rotten apples, like, for example, the ignorant kind who sees racism exclusively through a US-centric lens.
If anything, Tumblr has taught me so much, so I guess I was lucky to only know the "good side" of social & political activism on Tumblr, and never encounter the kind of rotten apple that DarthEmpress apparently had to deal with...
Some people tend to forget that not everyone is at the same stage of learning, activism awareness, and understanding, and feel the need to bash others and be super aggressive towards anyone who isn't at the same level than them, instead of actually engage in meaningful conversations.