Now see, that's a gross generalization.
Tumblr, like theColi, is populated by a wide variety of characters with disparate beliefs and backgrounds.
And just like theColi, it would be a mistake to judge the site based on the opinions of a very vocal segment.
Everyone here isn't homophobic/transphobic, small-minded, and self-seeking.
But you wouldn't know that if you only judged theColi based on TLR.
Likewise, there are plenty of self-styled social "activists" and "educators" on tumblr, regurgitating rhetoric they don't completely understand the foundations and philosophical principles of, but it's no less of a wonderful website because of it.
Just like here, you can tailor your experience by blocking, filtering out, ignoring, and simply not following any of the content you don't like, and supporting the content you do.
More to the point, I'm on tumblr because it's a wonderful repository of creatives and their work.
I like to think of myself as a creative too, so the blogs I follow inspire me, whether it be style, art, philosophy, poetry, animation, politics, etc.
And they have THE best collection of free NSFW material.
Plenty of amateur porn stars disseminating their work for internet fame.
Countless gifsets of professional debauchery in the genre of your choosing.
But of course, I peruse such material
strictly for research purposes to enhance my writing.
P.S. Your statement was also a jab at some of the female posters in this very thread who I am sure have managed to produce at least one productive thought in their life and yet still run blogs on tumblr.