Parents are not supposed to prevent their children from engaging in (sexual)relations. Rather they should make sure it's done safely, and with full knowledge of the possible outcomes. While this is some liberal bullshit, effectively you can't prevent children these days from engaging in sexual acts since you're not with them 24/7 or can control them 24/7. Hell, one of my ex's told me she first blown a dude at the age of 12, and she came from a strict catholic family, now what does that tell you? 
It tells me that despite their Catholic faith they were shitty parents. Shitty parents run the full spectrum and going to church doesn't mean you know how to raise kids.
And of course you can prevent children from engaging in various behaviors. What's wrong with you? It is natural for a person to be selfish, have bad manners, even be cruel. We are not born angels so decency, civility, manners and goodness has to be taught.
Both my parents are dead but the lessons and values they taught me are still with me, influence my behavior, and I still listen to them.
It's people like you that has abdicated their parental responsibilities that has given us what we have today. The changes in our society today compared to a couple of generations ago just didn't come out of thin air.
Great for teenage boys that there are tons of parents like you raising daughters. At least, I'd be polite so when I leave your daughter's room after fucking her in the ass raw (so I don't have a baby with the whore) and having her lick my cock clean I'd give you a wave and say, "Thanks Pops! You're a way cool Dad."