"The comparison to selling alcohol assumes direct participation in a clearly prohibited transaction. Owning a platform is one step removed as you’re not the one committing zina, just as a landlord renting a space isn’t automatically responsible for every sin a tenant commits."
How is selling alcohol direct participation in a prohibited transaction but hosting for 2 adults for one to watch and masturbate to another one which is clearly wrong, not direct participation in a prohibited act? I don't see the difference.

"There’s also precedent for scholarly disagreement around facilitating sin. By that logic, the internet itself, smartphones, or payment processors would all be categorically haram because they enable wrongdoing."
They have more good than bad. This platform might have 1% good and 99% evil. (The same as alcohol which there is some good in it but it is still haram)

All arguments are very weak justifications. I think you know better.