First of all, I am very much against exploiting under aged and emotionally immature girls to pose nude or enter the sex biz. The decision made to enter the sex biz. must be made by the girl herself in a calm, tranquil manner without any form of persusion from external forces ...
Nonetheless, to choose between two evils, it is definitely better for people to look at this kind of pornography and fantasize about it instead of having them lurking the streets, hanging around playgrounds and parks trying to harass little innocent girls ...
From an economical sense, it is totally "moral" to exchange the revealation of the girl's physical charm for money. Yet, on a humane level, it is immoral to exploit young girls making them pose without them knowning what these pictures are taken for.
Personally, having a foot fetish, I love feet with smooth flawless soles. The Net is loaded with pics of "smooth flawless soles" and feet of underaged girls. Yet, I get really turned off once I know it is the feet of a girl under 18 ... its just nasty and disgusting ... once I find out its an underaged girl, my dick just softens quicker then anything ...
Of course, one can argue that "age" is just a number and it is the actual maturity and mental development that counts ... an "underaged person" generally speaking, will not have the maturity of an individual who is legally "aged". Furthermore, some would say that we are sexual since the day of birth, and its just that the hormones just haven't "done their stuff yet" ...
I guess, the best answer would be, if she's got a bush and has mental and physcial signs of a mature adolescent/adult then she is "fuckable" ...