Gays in the Military

It's time to acknowledge the obvious.
We already have gay people in the military. We always have.
And despite that I have never heard of one report of some sort of gay related wave of sexual harassment or inappropriate interest.
What I hear is that the troops might not like it.
There's lots of talk about good order and discipline and unit cohesiveness.
And some talk about troops in some communal shower being worried that a fellow soldier/sailor is checking out their ass.
It's like they have no memory.
In 1947 President Truman ignored similar advice and ordered the Armed Forces to become racially integrated. And they did. It wasn't perfectly done. Racism exists in society so it exists in the military. But by all accounts, the Armed Forces did a pretty good job of forcing those whites in the service who didn't want serve with blacks as equals to either accept it or get out.
And it worked.
I remember growing up as an Air Force brat seeing people living together is something approaching harmony. It was clear that, no matter what a person might think, active overt racism was not acceptable any more. I was a kid, I am sure that there were things that happened that I didn't hear about. But by the time I joined the Navy, race was much less a factor in the Armed Services than in the population at large. We weren't that far from a black man as Chairman of the Joint Chiefs of Staff.
When I joined the Navy (1976) we were going through much of the same thing as women were more fully integrated into the Armed Services. They were serving on other than hospital ships in almost every speciality. They were flying fighter aircraft. Many similar arguments were made about integrating women then as they are making about integrating gays now. There were concerns that men and women would form relationships and those relationships were interfere with good order and discipline. That debate goes on since we still don't have women serving in infantry units, but almost all the disasters predicted by those opposed to what integration we have achieved didn't happen. There were incidents like Tailhook, where some people failed to recognize that the world had changed. But over a fairly short period of time, those problems mostly disappeared.
And now we are discussing acknowledging what is already true and contemplating stopping the insanity of punishing people purely for being gay. The utter stupidity of telling honorable patriotic Americans that they are not good enough to serve in the Armed Forces of this country simply because of who they love.
We hear much the same arguments we heard about blacks and about women and those arguments then were wrong and the arguments now will also be wrong.
How/Why is it defendable to allow some people's prejudice to determine that some other Americans aren't good enough to serve?