"The other day I discussed with an antiped who conceded that, while children cannot legally consent to sexual acts with adults, they are nevertheless capable of literally consenting—that is, of willfully permitting an adult to engage sexually with them. However, this person retorted that, though children can literally consent, antiped laws operate under the assumption that "children don't know better." Their ability to consent, according to him, "doesn't make it any better." (Quoted are his exact words, by the way.) Needless to say, I was flabbergasted upon hearing such a ridiculous argument."
The argument is not ridiculous. It is reasonable. The flaws in it are finer, and need more detailed addressing.
Note that even when adults are victims, fraud is a fundamentally consensual crime. When the victim never consents, it is robbery or theft.
"First of all, it is unclear what ethical relevance knowledge has when it comes to adult-child interactions in general. Indeed, virtually all such interactions involve a considerable difference in knowledge between adults and children with respect to the joint activity being pursued. For example, when adults play chess with inexperienced children, they possess more knowledge regarding legal moves, opening strategies, and basic rules. It would of course be silly to claim that this difference in skill makes chess games between adults and children unethical."
The idea here is that virginity/chastity is an expensive long term asset, like a house or education. In case of sex, it is assumed that the child suffers a great loss, and the adult benefits. The fact that the child consents merely proves "fraud" - no reasonable and adequately informed girl would give up her chastity/virginity, therefore her consent just proves she was cheated by her partner who benefited from the deceit.
Not the case with chess, because losing a chess game is not as harmful as losing virginity. Nor is a girl a slut for losing a chess game.
So what makes sex between children and adults unethical is supposedly the large loss to child.
" As usual, this person failed to clarify what, exactly, there is to "know better" about sex that makes childhood ignorance about the matter ethically relevant exclusively with regard to sexual interactions with adults (and not with other children). These people routinely parrot this baseless idea, which they apparently consider a truism not requiring any sort of elaboration or support."
There is a partial reasoning. If the less-informed party suffers a large loss and the better-informed party a modest benefit, this suggests fraud by the better informed party. If both parties are equally ignorant then the party benefiting can make a defence that the harm was unintended and done out of ignorance.
A problem with this if that if you claim serious harm, mitigated only by ignorance and therefore lack of intent of perpetrator, should sex be treated equally with other injuries? Like, a 13 year old boy who playing recklessly breaks the nose of a 13 year old girl, vs. the same 13 year old who playing recklessly breaks her hymen - in the latter case, should the girl be allowed to plead that she loves him, wanted to go all the way and got an orgasm?
"Secondly, this notion that "consent doesn't make" adult-child sexual interactions "any better" smacks of child rape apologia. Basically, this person believes that consensual sexual interactions between adults and children, which may or may not result in immediate or later psychological distress, are no more ethical than forcible sexual interactions between the two, which all but guarantee not only immediate as well as lasting distress, but considerable and even debilitating trauma!"
The question is - what is the damage? Mental distress, or objective loss of assets such as chastity?
Is defrauding a victim out of $ 100 000 any better than stealing $ 100 000?
Note that damage from fraud is still the same if no distress is caused.