To be fair, wanting to cheat on your partner to such an extent you'd set up an account on a website dedicated for that is already a step too far for many people barely any less bad of an act than the actual act of cheating.
I mean we make countless bad decisions as humans, many of them rash last minute decisions in a time of desperation.
Given the ease of just making an account and talking to someone vs actually going through with something I feel like just being on a platform like this is villainizing what could have been a moment of weakness. But that doesn't mean that you would have gone through with it.
I would also put out there that there may be a decent subset of people that just the idea that someone might be into them without needing to actually do anything beyond that, is enough.
I fully acknowledge that there is a lot of nuance to this, but I would hope that as a society we could acknowledge a huge difference between a bit of fantasy/role playing and actually going through with something.
It's like flirting when your partner isn't around. It's bad (assuming it isn't something you've agreed upon), but if you stop it before it goes to far it's not as bad as going to bed with somebody.
While the long term intentions (infidelity) might be the same, social barriers prevent many people from taking it forward. Signing up on a website is something a lot of people do for a lot of things and making that the entry point to something exciting and forbidden is good marketing at best and psychological manipulation at worst.
For some (perhaps most) people, just creating an account and taking a peek is usually not enough to push them over but for many others, it's enough to start a chain reaction that will end up somewhere which will have real consequences for them and multiple people related to them. Not a good idea and a company that's making money off of this without even considering that is not very ethical in my estimation.
Especially if maybe they were just watching porn and briefly in a horny state wanted to check something out. Post nut clarity is a thing.
There is just such a large number of events and thought processes between a last minute rash decision to make an account somewhere and actually meeting up with someone, not the least of which is the time and effort to make it happen. To say just making an account is barely less bad than actually going through with cheating is... wild.
OTOH, the makers of the website have designed it to push people to do something that's likely very damaging just to sell a product. And then topped it off by lying about what they're selling.