1. Rush of instant attraction.
2. People can justify anything if they really want to. Often the less known the easier to stay detatched.
3. Immediate gratification.
4. I think it does, actually. The depth of which can vary.
5. #3
6. I think this is a priceless addition... Would make a great topic on its own.
...if one had feelings and the other was making a notch on their bedpost, I can see a sort of dehumanizing effect. It's easy to say it was a mistake or a learning experience, but it taints future interactions.