There are plenty of people who feel the way you do - maybe its just because my friends and I didn't get upto anything we would be ashamed if our parents found out, but I do think its important to trust your children. The only reactionary parents in our group of friends belonged to the one friend that went wild at university.
As a Youth and Young Single Adult sleepovers were a huge part of what kept me active because they were what allowed me to travel and meet other Youth and Young Single Adults. I have very fond memories as a Young Single Adult of sleeping on the floor of a friends living room with 11 other women, with 5 men upstairs in the tiny bedroom - also remember the men used up all the bathroom time lol - similar things happened a Youth. One of my closest friends I have had since high school is male - even had sleepovers at his house.
I feel that its my job to teach my children but I also need to know when to let them go. And to trust them I feel children need to be respected and trusted to become trustworthy adults. They are not some weird alien subspecies they are actually small humans with an ability to make the right decisions if taught to do so. My Mum was very open about sex and I am very comfortable in my own body, when I made the decision not to have sex and remain chaste I did it with my eyes open - I want the same for my kids, my daughter already knows the basics about sex and babies as it came up looking at a 4D scan book when i was pregnant with my son.
I personally am very fussy about who babysits my kids only my parents, my Mother in Law, brother and bestfriend are allowed and even then I do not do it very often and my daughter has only ever stayed over at even Granny's once or twice. However do get to the point when I will have to take that chance that time will come when I know my daughter is old enough to say no or we have an open enough relationship that she can tell me if something did happen to her.
The man who trades freedom for security does not deserve nor will he ever receive either.