Although not entirely the same concept, this reminds me of a movie I saw called "Zerophilia" where certain people (i.e. "zerophiliacs") change gender after becoming aroused. As far as I'm concerned, if people don't feel that their physical sex matches their intended or felt gender, and they can naturally remedy the situation, I don't see why they shouldn't. The catch for me is...if they are same-sex partners in a same-sex relationship, why would they *want* to change genders?
So I guess my short answer is...if they switch gender out of love (for self and for partner) and for a sense of personal integrity, then I would go with "good thing". If it's for a whim, or to "fit in" and to "be normal", then I would say "bad thing". Very bad thing.
Besides, if God *really* wanted us to exceed the earth's carrying capacity for human populations, thereby bringing about our own ruin and leading to the extinction of countless other species along the way, we would all be born straight and fertile with extraordinarily high libidos. ;-)
Tangent: It might be a controversial theory, but it just seems to me that the closer a population gets to the limits its environment can withstand, the more widespread homosexuality seems to become as a natural population curb. That's not scientific fact, just speculation....Gaia has to protect herself and her children from destroying themselves.
Ready. Set. DEBATE!