When people are angry about injustices, they usually need a space where they can vent that anger with people who understand the sentiment behind the outburst and won't react back with stuff like "why so hateful" or "not all men" or "I actually love animals, especially with BBQ-sauce lololol" or "well schtatistically some races are just more prone to violence". Ugh.
Within these communities people can ventilate their emotions, and then go into the world (and witness the injustices) better regulated and not bring that explosive energy to people who may not deserve it or may not be able to hear it without misunderstanding it.
If you're not able to hear that type of rage without taking it personally or being upset or offended, I suggest those are not the communities for you. Not every community is. Let these groups have places for their rage, and be thankful they don't have keep that energy with them when interacting with the rest of the world.