Nope, that's not how this works.
If i walk into cake store i expect to see and be able to purchase cakes. If that cake store sells no cakes, despite being advertised as a cake store, the owner of the store doesn't get to say "it's your fault you expected us to sell cakes not mine".
OnlyFans has a known communally accepted reputation attached to it, if you do not meet those exceptions you are abusing that platforms reputation to lure in people to make a profit.
Ethan could have easily made a Patreon, they even allow nudity, Patreon has a reputation of supporting artists and small businesses. Survey one thousand people "what's the first thing you think of when i say OnlyFans" and the overwhelmingly majority will tell you "amateur porn".
I honestly don't care what he posts because I'm not going to subscribe, but this is a pretty lazy argument.
The cake shop is really a terrible analogy. If you walk into a cake store and they don't sell cakes, you leave. You haven't lost any money. It's not a scam, it's a shitty business plan.
It would be a scam if Ethan said "Hey, come subscribe and see my nudes" and then he never posted nudes. Despite Onlyfan's reputation to be for porn, that's not how it started. It was started as "a site where creators could monetize their content free of advertisers." There are fitness experts and others who have subscription services on Onlyfans. Are they scammers too?
And just because he could also set up a Patreon doesn't mean that is the only place he can offer his content without it being a scam. Patreon has a lot of rules about what you can put on their site (even if they do technically allow nudity), and part of Ethan's stated purpose is to provide himself a medium where he can post whatever he wants.