Yeah, there are some anti-contact arguments that are pretty simplistic and easy to dismiss. I make what I think there are better, persuasive ones. A few:

Regret may happen at any age, but there are some dramatic gradients with age. Prepubescents are just very rarely interested in sexual activity, and if they are it's more a curiosity than passion. Young teens may have an intense desire, but they can easily wait a few years for sexual activity with little harm (or do it with peers -- laws restricting sex between kids of similar age are insane). On the other hand, sexuality is so important to adults that it trumps risks. Also, young teens are in general much less good at discerning intentions of their potential partners.

Society doesn't like the idea of other adults conspiring to help their kids do things against the parents' wishes. (Radical youth libbers dismiss this, of course, but that's a separate discussion.) Secret sexual activity is a special case of that. If all adult-child sexual activity required uncoerced prior consent of both parents, indisputable child sex abuse would be down dramatically -- and so would all adult-child sex.

Age of consent laws are good for protecting young teens from indisputable rape. A girl or boy doesn't have to prove lack of consent -- if she says it was undesired and everyone agrees that sex took place, that's the end of the story. This knowledge deters rapists. On the other hand, teens should not be coerced into saying they were against something if they weren't, and as long as they say they consented, prosecutors should use discretion and not pursue a case.

We sweet, loving pedophiles in GirlChat think of wonderful relationships. The world is in fact full of men (pedophile or not) with much sleazier intentions leading to more sordid realities. The law can't tell them apart, so it has a strong motivation to prohibit all.