I imagine you've probably received a fair bit of email about your article, so I'll try to keep this brief and let you know from the outset that this one falls into the "appreciative but critical" camp.
I applaud the thought that you put into this matter and I agree with your friend about the positives of having any sexual activity conducted in a friendly environment, rather than a dangerous one (I'm not really entering into the complimentary stage yet, am I?). I don't envy the conundrum set you, as a mother of boys, who knows what it's like to grow up as a girl with boys around.
But (there it is!) I think your friend is right. I think that in wanting to protect these girls from their own indecision or loss of control, you're also protecting them from their own decisions and any semblance of mature control they might finally have wrestled back from society. It might have taken a great moving of internal mountains for these girls to finally be able to make the decision to accept an invitation to stay over at a boy friend's (note the space) house. Just walking through your front door (rather than clambering through your son's darkened bedroom window) might be the finishing line for them. They are probably prepared to walk through the front door in the first place because your sons are the kinds of young men they are (young men who know that "no" means "no", but who also understand that lots of other things also mean "No", like "I don't know", "Um", "
Enough about these girls. Onto the boys.
"There is a relatively straightforward relationship for boys between what they want, what they say they want and what they pursue – with sex, and everything else."
I think you're wrong about this. I've been a boy. I've been excellent friends with boys. It is not straight forward. Relative to girls, relative to anything. I'm not going to start asking where you get your ideas about this, but here are mine:
For teenaged boys there is almost nothing scarier than a teenage girl. Nothing. This does not get better with age. Look at the way women are treated by men, by society. Have you read Stieg Larsson? Apparently the working title for the first novel was Men Who Hate Women. This was not a new concept. But I digress - you know what I'm talking about.
The fact that your sons have girls who are friends puts them years ahead of their peers, I can guaranteee it. When they grow into young men, they will have left a large section of the male population behind forever when it comes to possessing the gifts that women can bestow upon others with their friendship: things like understanding, emotional intelligence and strength. They are already protected from the kinds of relationships which use up their joy and dignity. They will never be cowardly enough to use the words "slut" or "bitch".
I'll wrap up this "brief" (sorry about that) email with something reassuring: these sleepovers aren't about sex. They may be and eventually, they probably will be. But right now, despite the formal conversations between parents and the attempts at casual reassurance by partners, sex is not the only thing that two teenagers of the opposite sex can think of to do alone in a room together. Before the not-inevitable move to the least-squeaky trundle bed, there's probably a lot of learning going on.