So, it's not the underage kids posing as adults we have to protect
...rather it's the delicate sensitivities of agents posing as parents of underage kids posing as adults, and boy are they impatient! Not to mention the Daily Mail audience who've just read about this stuff. We've seen this before - the result tends to be that the organisation in question establishes a knee-jerk reaction to any and all complaints about conduct.
Investigations of the validity of those complaints tend to be too much bother and/or too expensive, and I notice there's no legal requirement for facebook to investigate at all, only that they allow a third party to review the process.
"Sorry, there was a complaint. We wont tell you who complained, or what they complained about, and frankly we don't care. In any case, your account has been deleted, and your personal information has been sent to the feds. Have a nice day!"
All in all, it's a very quick new way to for feuding facebookers to screw up each others' online presence.
On top of all that I know that I was (ahem) 'interested in erotica' many years before it would have been legal to for anyone to sell it to me, and if I'd been into 'older guys' (and if there had been a facebook back then), I might well have faked my ID to get hold of some. (In my young days, I discovered that mysterious benefactors would leave stashes of porno mags under bushes in the woods, or underneath train seats, so I and my friends never needed to buy any. Was I scarred by that experience? Well... I remember it happening. Does that count?).
Dangerous behavior, certainly, but I know I'm not unique, and It's important to recognise that while 'minors' are usually naive, they aren't always entirely innocent. It's a basic principle of cybernetics: In a complex system, control is a fantasy, there is only influence. (Nabokov's Lolita illustrates this beautifully, where Humbert ends up being the victim of his own fantasy).
This is part of a broader social/cultural problem, and simply forcing individual online communities to introduce 'stricter' rules will almost certainly make the online community more kid-friendly and less adult, which may even have the the effect of attracting more pedofiles with even more cunning 'grooming' strategies etc. Driving things underground merely makes them less visible and more frightening.
As for the romans... what about the polymorphous sexual culture of the ancient Greeks. Yep, they invented the concept of democracy, but buggering boys was considered a socially useful activity; a foundation stone of educating the next generation. It's a relatively recent thing that the pedofile has become demonised above all other evils. Worse even than terrorism, or mass-murder in most cases. Somehow I think, as a culture, we've painted ourselves into a corner with this stuff: Demons have the power we choose to give them.
I'm not advocating a laissez faire attitude, just a bit of sobriety.