Nature decided that so called "gays" (an artificial term, created in our modern times) can't procreate, so if you would make an island for them, good old Nature would answer with extinction...
(I think Nature is really discriminating here. Someone should sue It.)
Some heterosexual marriages are sterile, too.
In my country, children are (currently!) really fortunate: they are guaranteed to have a mother and a father (yes, I know already your objections), and, as psychology is able to demonstrate, this is still the sanest and most harmonic way to grow children.
Why do we always exclude children from this reasoning?