Good deeds don't make you immune from criticism. And are we really expected to give a by to the garbage you see on /pol/ and the like?

I mean, everyone who is an "internet person" basically knows that these sites are full of terrible things. But for 4/8chan the response is sort of a weary acceptance, a "we don't go to that dark shadowy place" from everyone who isn't part of that community. But when people respond to tumblr's flaws, it's usually much more vitriolic – people turn mocking that site into a sport.

If these were just niche sites it wouldn't be so bad, but chan culture is a huge part of internet culture as a whole. And so when we see them pulling raids like this for their own sadistic pleasure, and with hardly anyone calling them out for it, that's a huge problem.

Seriously, the whole point of this stuff is "I am going to find a way to make these people unhappy so that I can laugh at them." In any other context that wouldn't be acceptable behaviour, but if 4/8chan is doing it, then a disturbing large number of people will think it's hilarious.

It's because of the motives behind it.
tumblr does it to push their "everyone's beautiful" mantra.
4/8chan does it to piss off tumblr.