I could give a frak what gay people want to do (or anyone else for that matter.) If they want to join the military, by all means please do. Goes the same for marriage. You want to do it, you're an adult, you're not forcing people into it, and you are not directly hurting anybody, then you should be able to enjoy all the freedoms everyone is entitled to in the country.
Discriminating against somebody is an invitation for yourself to be discriminated against imo.
As far as evolution and nature/nurture goes;
Sure, there is a lesbian chic and metro dude thing going on now, and there are some people who turn to the same sex after suffering abuse, but I don't think that constitutes the majority of the gay population. Truth is being gay sucks. Who wants to chose to be a social outcast and not being able to live openly and having freedoms restricted?
Homosexuality has been found throughout history is prevalent in all the cultures I know of, even very repressive ones that.
Just week from the African nation of Malawi:
"A judge in Malawi has imposed a maximum sentence of 14 years in prison with hard labour on a gay couple convicted of gross indecency and unnatural acts.
The judge said he wanted to protect the public from "people like you"."
Strict laws in Kenya, Egypt, Iran, and Uganda is threatening to make it a capital crime. Yet gay populations persist. Why would anyone choose this?
I knew a kid from HS that ended up hanging himself as he was gay, didn't want to come out, and hated himself (as he wrote in his suicide letter.) F'd up man.
Evolution does not disprove gayness, as there are a lot of inherted traits and genetic expressions that are directly harmful to an individual's fecundity, but are conserved as the trait provides an advantage of the group. IOW, evolution is not limited by the boundaries of our imagination.
Take menopause for example. Women begin to have chances of birth defects rise exponentially from the age of ~30, where by 40, chances of failed pregnancies or abnormal children is likely. If evolution only played on individual fitness, then this trait should not persist. However, it may be more advantageous for the group for this individual female to stop her own reproduction an instead function as a matriarch or other role than is more beneficial to the group, even tho at her own expense.
Basically one needs to be very careful in assigning evolutionary directives or causes to traits or behaviors, as it depends on a limited human understanding of the genetic interactions and selection forces, which is often beyond our ability to easily comprehend.