You can see why this opinion comes out where it does. Judge Clifton begins the thing with a nice little summary:
"It is a crime to produce outside the United States a visual
depiction of a minor engaged in sexually explicit conduct and
to then transport that visual depiction into the United States.
18 U.S.C. § 2251(c). It is also a crime to attempt to produce
and transport into the United States a visual depiction of a
minor engaged in sexually explicit conduct. 18 U.S.C.
§ 2251(e).
In this case, we consider what happens when a defendant
believes that the victim appearing in a depiction is a minor
but the victim turns out to be an adult. That defendant cannot
be convicted of the completed version of the crime, but can
he be convicted of attempt? We answer that question in the affirmative: a defendant attempts to produce and transport a
visual depiction of a minor engaged in sexually explicit
conduct when he believes that the victim is a minor,
regardless of the victim’s actual age."
That holding largely follows from the nature of attempt crimes. Mistakes of fact don't generally stop you from being guilty of attempt. So there you have it.
Just note that -- as is often the case -- the real fights are in the footnotes. Particularly this one:
"This case does not present, and we do not decide, the issue of
whether a defendant may be convicted of an attempt to violate § 2251(c)
if he believes that the victim is an adult but the victim turns out to be a
minor."
Ditto for the substantive offense, right? I could easily see courts imposing strict liability for sex offenses with minors; e.g., you don't get to claim that you thought she was an adult.
The net effect of which -- if it comes out that way -- would be to make this a one-way ratchet. You're guilty if you thought she was a minor (even if she wasn't) and you're guilty if you thought she was an adult (but she wasn't).
