And that's where you're wrong. Arranging to have sex with someone you think is underage is a crime, even if no child is involved at all.
Yep. Just so we're clear as to what the crime really was and that no actual child was harmed in any way.
Now, given that, what should be the penalty? Life in prison (because we know these guys can't be rehabilitated)? Perhaps their face on national TV, a couple of years in state prison, then branded for life as a sexual predator?
For thinking someone was a minor?