But all of the objections…

Sexual activity between a man and an underage girl today is a very bad idea and risks serious delayed harm to the girl. The essential problem is secrecy. If she does not keep it a secret, then mandated reporter laws will wreak havoc on both of you. If she liked you, knowing that spilling the beans got you locked up in prison will be very distressing.

If she does keep the secret, she has to keep it for the rest of her life, since there are few if any statutes of limitation applicable to the situation. If she remembers it fondly, she has to constantly monitor herself to not mention it to the wrong person. If, on the other hand, she comes to regret it or feel conflicted about it -- which is very common for early sexual encounters -- she cannot get help from any professional to deal with her feelings without destroying your life and putting her through hell too. Confiding in friends puts her in great peril too -- and gives those friends a secret they have to keep in turn.

…in turn depend on the premize of criminalization.

Leave aside the question whether legalization is feasible (or even whether it is desirable) - if it did happen, none of the above would apply.

In my worldview, this is tied inextricably with why I don't think acceptance (of us) is possible without legalization. But I admit that is a bit of a leap from just this part of the argument. What is not a leap is that all of those possible and foreseeable harms are consequences, not causes, of criminalization.