What you're essentially saying is 'Adult content is hard because the US government is willing to lean on payment providers to enforce quasi-legal, anti-free speech policies.'
Have you considered adopting a federated corporate structure that would legally firewall off a "tumblr-for-porn"?
Most of the goodwill bonfire seems to have been caused not by Tumblr treating adult content differently, but by not even putting up a fight to provide a space for it.
Having a mirror world Tumblr that adult blogs could be kicked to would earn a lot of that back, while presumably amortizing platform development and ops over a larger userbase.
Surrendering because free speech is hard is never a good look.
That is literally the convoluted situation photomatt was trying to avoid.
I also think that the suggestion is hilariously naive. Presumably the founder/head of the company has considered a variety of incorporation structures.
One would think, but apparently neither Yahoo nor Verizon made any effort in that direction.
To the tune of putting approx $1 billion through the corporate paper shredder.
Given that track record of handling, and an ostensibly similar approach, I thought it was a valid question.
Arguably, that happened June 20th, 2013, the day the Tumblr acquisition was closed.