Well that's just a weird stance. Who cares how others treat sex if they're adults? You can treat sex as the most serious business; someone else's promiscuity doesn't affect that. It's like the "gay marriage will ruin the sanctity of marriage" retard-rants we heard. No, two men getting hitched has nothing to do with your own marriage.
From what I understand the 'casting couch' situation comes with a lot of pressure and coercion, so it's not really comparable to say a prostitute selling themselves. Look at it this way, when a prostitute is looking for work, the sex for money is known ahead of time. While an actress auditioning is probably not thinking "I'm going to have to suck a dick for this role." when going in; she's expecting to get the role on her thespian skills alone.
edit: Obviously I'm referring to prostitutes in my scenario above who are doing it out of their own free will and not being forced, which happens