Kiddie porn is illegal because kids are under the age of consent, if they were 18 there would be no legal problem.
Hmmmmm. Why 18? Why not 17? 14?
I mean, even the Libertarian Party doesn't believe in some arbitrary, government-mandated age. To wit:
"However, children always have the right to establish their maturity by assuming administration and protection of their own rights, ending dependency upon their parents or other guardians, and assuming all responsibilities of adulthood."
How about that?