The presence of homosexuality in all cultures and populations indicates that it is not simply a decadent western "choice". Additionally, same-sex behavior is well documented as a minority behavior throughout the animal kingdom; for example in domestic sheep, about 8-10% of rams are only interested in mounting other rams (and about an equal number are completely asexual, not interested in mounting rams or ewes). This can have significant economic impact on sheep farmers, but despite careful breeding, the trait persists.
So we see homosexuality very much like other complex traits, maintaining at a pretty constant level across time and populations. Which also shows us that the argument about humanity "dying out" is pretty, well, stupid. Straight people will continue to have kids. A few of those kids will continue to be gay. Since being gay is not a choice, the old canard about "recruiting" is based on ignorance.
The American Medical Association, the Psychiatric, Psychological , and Pediatric associations have all "de-pathologized" homosexuality. They consider homosexuality a normal human variation that in and of itself is not an illness or a sickness. It's a normal, if minority variant: like being a redhead, or a lefty. It doesn't hurt the people who have the trait, and it doesn't hurt the people who don't. Forcing people to deny it is harmful (and one of the reasons why the "Ex-gay movement" is so dangerous). This is another reason education is essential-- so people don't mistakenly try to cure the variant.
Gay folks are just as able as straights to make faithful and permanent commitments, and a big component of the marriage equality movement is to help people do so by providing the same social structures that support any marriage. After all, how stable do you think straight families would be without marriage? How faithful would young men be without this kind of structure? That's why in some disadvantaged communities, there is a strong movement to encourage marriage because of the support structures it provides struggling families.
What DOES cause problems for the gay community is marginalization and bias and bigotry. Fortunately for younger GLBT folks, things are a lot better than they used to be, but rejection of gay youth by their parents is still a major health issue and runaways and suicides are more likely to occur in gay kids. Let's hope we move to a point where we can be accepted simply as part of the wonderful varied tapestry of humanity, and not try to fit people into simple binaries.
A minority behavior is not wrong simply becuase it's the minority. It's not wrong to be red-headed, or left-handed.
So, what color are your eyes?
There are a couple of excellent books for those interested in this topic. First is an exhaustive record of same-sex behavior in animals from fruit-flies to chimpanzees, Biological Exuberance by Bruce Bagemihl. HIs work shows how strongly observer bias leads to value-judgment interpretations, that are not scientific. The role of the scientist is to report the observtaions, not decide to ignore some of them because they don't fit a preconceived social notion of complementarity.
Second, Joan Roughgarden's book Evolution's Rainbow is a more detailed analysis of gender and sexuality in behavior. As she points out, many species have members fulfilling multiple distinct roles, not simply a sexual binary. Roughgarden also spends some time discussing varied sexual behaviors in mammals, including our cousin-primates, the chimpanzees. While I don't agree with all her points, which have a distinct agenda of her own, she offers much to think about.
To read this entire series in order, visit the Genetics Page.