This is not a 'given'; this has been argued for centuries. I have met some people who were simply 'odd' from childhood, who later announced that they were gay. In my experience, these people no more chose to be gay, than they chose to be white, black, asian or indian.
Yes, there are some who do 'choose' to be gay; but if you accept that about 2-3% of the population is born with a defect (blind, no arms, legs, deaf, mute or otherwise), then seeing a population of gays that does appear to be within the 2-3% margin seems to fit. I do not hate gays, I pity them.
Who would chose a lifestyle that will inflict pain and humiliation not only upon oneself; but one's friends and families as well. A lifestyle with a very high rate of suicide, alcoholism and one that seems to invite torment and physical abuse? Some gay men marry; have children, and try to fit in as a 'normal' person would; and we all know what a mess they leave behind when they decide that they are living a lie.
Yes, there are SOME who decide to follow the gay lifestyle for kicks and to fulfill some kinkiness; but can you imagine actually preferring to have sex with a member of your same gender? I certainly can not.