it might not be harmful for them to lose their childhood, but it is really, really really fucking wrong. a kid should only have to think about playing, making friends, and doing homework. they shouldn't have to think about the things that come with sex, that's just wrong.
and no, danger isn't a good reason to outlaw bestiality. if danger was a good reason to outlaw something, you'd outlaw smoking and alcohol.

Yes, yes you would. And I think smoking should be outlawed, and I think it will be, with time. Alcohol has other benefits - social lubrication, mostly, that have value to society. Bestiality does not have any value beyond baseline.

So I assume you're okay with people having sex with anyone post-puberty, given your idealistic 'playing, friends, homework' trifecta. So you've lowered the bar to ~12. Logically, I used to agree with that. But I've come to understand that sexual interactions are not innately harmful, not matter the age at which they take place. These organs are functional in all regards except reproduction from the moment we're born. I would rather see parents, like bonobos, use pleasure to calm their kids, instead of violence. Only in this fucked up post-agricultural culture do we think that violence is a more acceptable means of disciplining children. If you're so worried about mental effects, maybe you should start there.

So smoking should be illegal, but parents disciplining their kids by fucking them should be legal?

Context matters. If harm is caused, it needs to be justified with a benefit. The benefit to smoking is feeble at best.

I'm not advocating for rape. Rape is simply a destructive act. But my disdain for rape does not translate into a disdain for sex, or other sexual interactions. In the context of this argument, I would say sexual interactions to calm children would be permissible and preferable to spanking or psychological abuse in the form of isolation. That doesn't mean rape, beatings, or violence.