This is no worse than Discord just banning NSFW content wholesale throughout the platform (which they would be entirely within their rights to do). It's a big fat nothingburger.
It would be in their rights to do it.
Its users who value their privacy will be in their rights to leave and we will.
They have a right to ask for my passport and SSN. And I have a right to say "hell no" and delete my account in response.
It's not a nothingburger; it's a massive collection of personally identifying information.
Except it is scarily easy to find servers which openly have minors selling NSFW content. Or BDSM servers targeted at "14-28 year olds".
I'm sure the owners of Tumblr thought the same.