That being said there is a prevailing assumption in the Western world that homosexual people are simply 'born that way.' That their sexual temptations are 100% genetic, and they can never find fulfilment in life unless they act on those temptations. The assumption is that if you are tempted to 'be gay' then you must act on it, or else you are 'living a lie,' and going against nature. Much attention has been given to counter this argument, by pointing out as I said above that ultimately it is our choices that define us, not our temptations. Christian doctrine teaches us that sexual fulfilment cannot be found outside of God's natural plan for us, regardless of our temptations, and therefore we should seek God's will to find that fulfilment. There are of course those who try to twist Scripture and the authority of Church teaching to justify their homosexual sin, but for the most part, historic Christian sexual ethics are just discarded in favour of an evolutionary mindset that nature simply selects some people (randomly I suppose) to be homosexual. The assumption is if one experiences persistent homosexual temptation, than obviously God (or the gods, or mother nature, or whatever) wants that person to 'be gay.'
Rather than counter this argument, The Catholic Knight will now play devil's advocate and reason it through to the most logical conclusion. Let's suppose the homosexualists are right. Let's suppose it really is all about evolution and natural selection. Let's suppose people are predestined from the start, by genetic code, to 'be gay.' Let's just assume they are right and Christianity is wrong.
Now let's take this to it's most logical and natural conclusion.
Nature puts the sexual desire into all creatures to propagate the species. In other words, nature has only two rules. The first is 'make babies or die.' The second is 'only the strong shall survive.' So if we are to assume that nature is naturally selecting some people to be 'gay' than we can only assume one thing. Nature doesn't want them to reproduce, or at the very least, nature doesn't want them to reproduce as rapidly as 'straight' people. Because you see, the sexual urge in straight people remains the same. So unless they are artificially contracepting their natural reproduction, they will likely reproduce much faster than a gay person who is wasting his/her time having sexual relations with members of the same sex.
So why would mother nature want some people to have more babies and other people to have less? The second law of nature supplies us with the only logical answer, as cruel and insensitive as it may sound. Nature must only want the strong to survive. In other words, something must be genetically wrong with the gay people, which is why mother nature is trying to slow their reproduction and thus weed them out of the population.
When we eliminate the Christian explanation that temptations do not define who we are, this is the only logical explanation for the homosexual phenomenon. Nature has selected their gene pool for extinction, or at the very least, a significant population reduction.
I don't know about you, but if I suffered from homosexual temptations, I think I would prefer the Christian explanation over the genetic explanation. That's just my thoughts anyway. Maybe some people prefer to think of themselves as genetically inferior and therefore selected for extinction/reduction.