I am with your friend. We do not allow sleepovers until age 13 or 14...even then, it is selectively. Yes, they can be lots of fun, but it will not ruin your daughter's life to miss out on them. Some of the things that can happen at sleepovers CAN ruin your daughter's life. Your friend knows and understands this because he has seen it first hand. We made this decision because my husband has counseled men in Christian rehab for drugs and alcohol and heard sleepover horror stories time & time again from these men who were numbing out from their pain with drugs and alcohol. Nothing may ever happen if you let her, but our feeling is...why would you unnecessarily put your child at risk so they can have "fun"? You will never KNOW the parents of your children's friends. Some people never KNOW their own siblings enough to know that they would/could harm their own nieces/nephews. Happens all the time...ask your friend. You aren't letting your child "live under a rock"...you are doing your job as a PARENT...protecting her. When she gets old enough, she will understand.
Google: Sleepover molestation
For those who think they "know" someone (neighbor, church family) well enough to let their child sleep at their home, here is an excerpt from an article about the BTK Killer, Dennis Rader:
"Rader is accused of killing, among others, a family of four; a widow who lived just three doors down from him; and a young woman whose brother fought with BTK and survived.
"I can't believe what they are saying is the Dennis Rader I've known for 30 years," said Paul Carlstedt, whom Rader replaced as church board president in January. He thought of Rader as "a very good person."
Just days before his arrest, Rader brought spaghetti sauce and salad to a church supper, though he was unable to attend himself, Carlstedt said."
If people who "knew" him could never think of him as a serial killer, why would anyone suspect their "nice" neighbor of having a thing for small children? The truth is, you never really KNOW what someone is capable of. Don't shelter your children, just protect them by not putting them in potentially harmful situations.