It's actually the opposite - SubscribeStar has proven that they will not bow to this kind of pressure. That's why you can't use PayPal there; PayPal tried to exert pressure and SubStar told them to get lost.
(Not sure why you're using age verification as evidence of susceptibility to pressure; that's just a standard legal check that every adult site does).
It's not great as a marketplace, granted, but that could be easily fixed with a single "one time pledge" change; not too difficult if they went that route. I doubt they will, but hope springs eternal.