And you think religious parents are incapable of doing this?
In order to keep their kids somehow shielded from this, lots of parents homeschool their own values into their kids - and just like in a normal school, sometimes they come out fine, sometimes they come out disfunctional.
My take on it is that if you love your child and truly care about their happiness, and you trust them and have raised them right, then you owe it to them to give them the most honest and straightforward information you can, instead of working to protect your own self interests.
And you're dead wrong on homeschooling. Parents don't homeschool their kids to shield them from social experiences or just to ensure that they aren't having sex. Parents homeschool because they're thoroughly dissatisfied with the school system. Sometimes it's moral stance; other times it's safety issues; others, it's quality of education provided. In most cases, you'll find it's a combination of those things.
Given the way schools are these days, there's evidence to back them up.