Just adding my voice to the calls for Itch.io to reverse this appalling decision.
While the driving force is the payment processing companies, it is still down to Itch to take a stand against censorship and in favour of adult content. Ideally, other platforms with a bigger market share (*cough*Steam*cough*) would have done so already, but someone has to, and Itch - a platform for indie and solo developers, who often explore gender, sexuality and other "adult" themes in their works - is not fit for purpose if it won't any longer take that stand and fight back against puritanical organisations trying to restrict human expression.