Tumblr is a vast network that, among other things, provides a place for people to be themselves. While there are things that safe mode could be quite useful for (no one wants porn to come up at work), posts relating Gay, Lesbian, Bisexual, Trans, and other forms of Queerness are not the same as pornography. By stuffing these posts into a box, you are basically protecting people... from the mirror. The vast majority of the Tumblr userbase supports LGBTQ rights, and many are LGBTQ teens and college students who are in the closet at home and need a place to safely express themselves.

Please keep the NSFW stuff to porn, graphic violence, and if you want to go out of your way to know your userbase, perhaps include the "tw" (trigger warning) tag - though that one means different things to different people.