Problem
Tumblr, after years of being a space for nsfw artists to reach a community of like-minded individuals to enjoy their work, has decided to close their metaphorical doors to adult content.

Solution
Stop it. Let people post porn, it's 90% of the reason anybody is on the site in the first place.
Or, if you really want a non-18+ tumblr, start a new one with that specific goal in mind. Don't rip down what people have spent years working on.

Personal story
I'm a NSFW tumblr artist who has the vast majority of their viewership (and thus, potential for income from commissions and such) on Tumblr. With tumblr being taken down, a LARGE portion of my viewerbase will go with it, and not only will this hurt people like myself, who rely on this income to live, but it will also mean the people who DO want to view that content no longer get it.