--snip--
This is cheating, and it's objectively wrong, and in the long run it only reinforces this behavior, and they might start cheating in real life too. And cheating is a very serious issue, it ruins families, which in turn tremendously screws peoples lives, including and especially children's. Just think twice before suggesting such services to your friends - do you want to be complicit in it all or not? I think a good friend would never do such a thing.
Look, those who never leave their families even after cheating at their back and just pursue their responsibilities as a good person shouldn't really be blamed for their needs. OP is not doing a social work here, if she'd have been doing it, I'd also recommend to join the same to my friends as well and they would happily do a charity no matter who the person is. It's everyone's choice and a good friend is also the one who makes both the ends meet for his friends. I'm not gonna ruin anything for them as far as they don't commit any physical relationships with such personalities.