The percentage of the population that claims to be homosexual is actually less than 3%. IMHO it's an insignificant and unpredictable factor.

I think the real population "adjustments" will come in the form of uncontrolled epidemics, wars, radical climatic changes, and the big question mark of what happens when the lack of support structures will reach critical mass.

Technology will save us in some respects, but will likely kill us in the end.