Can someone please explain the difference?

[Rev. Rye]

It's just as much a choice as it is for heteros to be attracted to the opposite sex...

It's a 100% natural urge, irrespective of its origins... (nature/nurture)

Technically, the choice is acting upon the urges and embracing them. But, like I said, it's really not much of a choice.

Of course, what makes it okay isn't that it's "natural"; for instance, what little research has been done on pedophilia suggests that its origins may be inborn like homosexuality. However, in this case, the key difference is that homosexuality isn't really all that harmful in and of itself (the anal sex may do a number on your bowel control [which is why some gay people, Stephen Fry among them, do strictly oral], HIV is still a problem [if relatively easy, but not too cheap, to manage], and you still have to deal with homophobia, but that would seem to be it). The argument shouldn't be just that it's natural. It should be that it's inborn and mostly harmless (and I say "mostly harmless" mostly because of the three issues above, and the Kevin Spacey types that I suspect occur in all sexual aggregates in some proportion or another.)