Let me tell you the tale of a time before your time on the internet.
Back when Gaia was the big newfag boogeyman, Youtube was a young little site, and there were Sprite Comics as far as the eye could see. All you see about that kind of shipping? It was there, it was there for years, it was there longer than you've been browsing. Most often it congregated on Deviantart back when that had competition, with all the poorly drawn, decently drawn, and even occasional well-drawn bits of shipping art for everybody. Lots of it gay. LOTS of it really fucking gay. Lots of it even the ancient Greeks, in the middle of fucking young boys while debating philosophy, would request they tone it down.
Tumblr is just one more outlet those kinds of things, anon. This time with a political bent to it, but even that existed before the site became what it is today.