I was following you until you got to "Otherwise restricting them is tantamount to enforcing somebody else's sense of morality on them."
Don't you think our laws are just filled with examples of (en)forcing someone's sense of morality on everyone, including upon those that disagree? Is that necessarily a bad thing? Some might not agree with the minimum age requirements for people to perform in porn vids, but some/someone's sense of morality gets imposed, whether they like it or not, and if they defy it, they're in trouble. In most places you can't just torture an animal on a public street (or at all, for that matter), have sex in a public park, purchase or consume heroin, or drive your kid around with them sitting on the hood of your car. Those who think these things are acceptable are, in effect, having "somebody else's sense of morality" (en)forced upon them...