There's nothing wrong with a little good-hearted promiscuity in the bedroom. The real issue here is the lack of communication between Mitch and Heidi. The time to tell your significant other that you're into orgys is NOT after the naked couple comes out of your bathroom with blindfolds on. I can't imagine that would be too easy for anyone to process, especially when you have a butt-naked man with his arms around you after he yells, "Gotcha!"
On the other hand, maybe Mitch just needs to lighten up and not be so quick to shut down ideas just because they're a little unorthodox. After all, it's purely sexual.