Read other letters about this article
"...the adolescent sexual-social hierarchies that develop in larger, unrestricted schools, which we're seeing here can be extremely damaging to both sexes."
You can say that again!! :)
And guys, women really do not want guys who already have a woman. We really, really don't. Just like you probably do not prefer women who already have a man. This alleged phenomenon you're speaking of is the result of two things:
1. Most women realize that she often CAN'T be friendly with a single guy without having that guy assume she wants him. With a coupled guy, women figure they can engage with him without the friendship/exchange heading into sexual/romantic territory. My boyfriend makes this mistake. He thinks that most women who are friendly and interested in talking to him want to jump his bones, even though I can see pretty clearly that it usually isn't the case. But he obviously gets a kick out of it, so I don't say anything.
2. Wanting what you can't have -- in general, when you CAN'T have something, it suddenly seems to be available all around you. Taunting you! So a guy with a girlfriend who can't sleep with other women suddenly experiences the world as full of gorgeous, available women. I actually once overhead a conversation between two guys who were agreeing that when they are single and go out, all the women are ugly. But as soon as they go to a bar when they have a girlfriend, the place if crawling with hot chicks. I thought that was hilarious -- they were being serious! As if the universe was actually conspiring against them.
It's just a matter of perception.
Also, as to the contention that women hit on coupled men more often even when the man is alone and the woman doesn't know he has a girlfriend, I don't doubt this is true. He is more likely to appear happy and relaxed, and to not be leering, if he has a woman. Which is all much more attractive than the opposite.
For both men and women, after you get past pure physical beauty, there is nothing more attractive than someone who seems happy, engaging, and comfortable with themself.