Well consider this. Maybe being gay isn't a mistake, but rather a built-in population control. Check this out (from wikipedia)

In the wilderness, the problem of overpopulation of species is often solved by growth in the population of predators. Predators tend to look for signs of weakness in their prey, and therefore usually first eat the old or sick animals. This has the side effects of controlling the prey population and ensuring its evolution in favor of genetic characteristics that enhance escape from predation (and the predator may co-evolve, in response).

In the absence of predators, species are bound by the resources they can find in their environment, but this does not necessarily control overpopulation, at least in the short term. An abundant supply of resources can produce a population boom that ends up with more individuals than the environment can support. In this case, starvation, thirst and sometimes violent competition for scarce resources may affect a sharp reduction in population in a very short lapse (a population crash).

The human race is pretty awesome. With our big brains and opposable thumbs its no wonder humanity quickly rose to the top of the food chain. We essentially have no predators which makes us susceptible to this problem of population booms and the subsequent problem of population crash. While overpopulation is a looming problem, it might be even worse if we didn't have 5% to 10% of all people being born with no desire to reproduce. You could even argue that homosexuality is a form of evolution. In an environment where a species has no predators, to continue their overall survival for as long as possible, its better for nature to limit their overpopulation in whatever way it can.