Just look at Patreon and their continued stuggle with NSFW artists. I briefly worked on a similar smaller site that allows for artists drawing explicit things, and our payment processor would threaten us weekly to cut us off for arbitrary reasons. The chargeback/fraud rate did not differ based on the user drawing explicit content or not.

I can't point at data, but there's plenty of articles and reports, including this from the EFF: https://www.eff.org/deeplinks/2020/12/visa-and-mastercard-ar...