The problem with Tumblr is that all the people who feel slightly "outcasted" go there, and then they make the stunning realisation that Internet allows you to be anybody you want, and so they choose to cosplay as forgetwits.
4chan spamming them probably made them feel all giddy inside because it's a chance to get attention by making huge "rallying calls" that make them seem like heroes, when in reality they're probably a 14yo teenage girl going through puberty with social awkwardness who hasn't quite figured out that telling people that you're "gay and proud of it, pls respect rights or die in hole rapist scum" is just as bad as christian richardheads saying "gays are anti-christ burn them all".
Tumblr is an okay platform, but I'd much rather spend time with the 4chan, Reddit, BLF etc community because at least the far majority have basic common sense.