Honestly I've been playing around with the idea that perhaps certain websites' mechanics attract certain people or even just encourage certain behaviors.
It's the reason why Twitter's shitstorms are caused by people doing micdrops and vanishing, it's the reason 4chan created /b/, and it's the reason why you have the infamous MRA thing over with Reddit.
Tumblr is a mixture of blogging and social networking where you get very isolated communities of people who are trying to express things. It's basically livejournal with a quicker share feature. So you get a lot of personal and painful stuff from people where that's one of their few places they can express it, while at the same time you get this stuff overlapping with a lot of media being reposted there. In addition, you get people popularizing their image due to the blog approach.
As such this kind of encourages SJW in several ways, but I hesitate to call that a breeding ground of actual social justice discussion, given that it's not really a place of empathy so much as a place where there's a community for social issues and an easy way to show you care without committing too much to a cause. This is why controversies flare up rather than really stay constant.
It's actually really easy to avoid a lot of drama on that site, same with every social networking site, but I feel it's important to address WHY it gets that reputation.
I mean, take a look at the Escapist, where you have a system where discussions are born in the first couple of pages of a thread, while the later pages are either continuations of things that began in the early pages or they're responses to the OP. You get a lot of people here who then fire off a single post and leave the thread, and users are encouraged to post in the newest stuff.
We value getting our 2 cents in and then leaving, not really looking over a thread for weeks. It's why we get so many "Am I the only one..."s because the site is set up so that what is new is what's at the forefront of the discussion, and so we don't hear as many matching opinions. Meanwhile the hate for this brought on by the large amount of these posts seems almost inherited by new generations of Escapists as they're taught this question is deserving of sarcasm due to this response being so common.
The site's mechanics are also why you'll always see a select group of users at the front page of every article for set periods of time. The site is all about moving to the latest thing.
Just some food for thought on social networking in general.