Just give the game a mature or 16+ rating or whatever ratings there are, so the prudes can stay away from it.
Oh wait: This game, and the fallouts,
are rated M. Gosh, maybe the prudes should stay away then..

Natural part of life as a teen? I work in the human services field and see enough teen pregnancies because parents don't address it. These decapitiations are not real folks and we do know the difference between reality and a magical little world that we do not live in. Going to a nvde beach on weekends is a little different than promoting six and hearing language that we don't repeat in our home.
Actually, it's usually either the kids who get raised in prude environments or the kids who get raised in wrecked environments who run into pregnancy early.
If the kid knows what the dangers and complications are, it won't get pregnant. It will be more able to make it's own conscious decisions. It's less likely to get into these things secretly and it will be especially less likely to engage in sixuality to rebel. Besides that, you can't expect to keep a teenager with hormones boiling over through it's ears away from those things. That's like living in a dreamscape, sticking your head in the sand.
And.. uhm. decapitations might be an overstatement. But themes like drugs, murder, exploitation, theft, corruption are very much real. And the game very much incites these. At least with sixuality, when done properly, there's love involved. The things you seem to care less about in your education don't have that, they are the opposite. I will only have my kid play M rated games with proper guidance, and I won't discriminate in real world growing-up issues, certainly not make 'em booboo, and I certainly won't give the message that murder is more acceptable then sixuality.