Then s/he is also fundamentally incapable of having criminal intent and cannot be charged with a sex crime. You can’t have it both ways.
And, BTW, many countries and states disagree with your stated assumption of the purpose of these laws. That is why they do make a distinction according the ages of the parties involved.
I agree.
... many countries and states disagree with your stated assumption of the purpose of these laws
I didn't say anything about the purpose of the laws. I remarked upon the reasoning supporting such laws, at least in general in the United States.