This thinking is completely opposite the "God made me this way" pablum that today's homosexual activists push. I think everyone recognizes that Man has a sinful nature and we are tempted to do many things that we should not do (stealing, violence, perversion, etc.). The point of being a moral person is that we abstain from the acts which are improper.
The people who claim "I was born this way" have simply given up on behaving in a moral manner. They don't even try.
I think Vidal is right on this point. However, people do differ from each other in their particular vulnerabilities or individual temperaments, and the word "homosexual" (or better, "a man who experiences SSA") can be used in that sense to describe a person with that particular vulnerability.
There are some men who would never feel inclined to engage in sexual relations with another man under any conditions. There are some who would feel so inclined under conditions of stress, an all-male environment, and isolation from women (armies, navies, monasteries, prisons). There are some who "feel" this inclination during early adolescence but not upon full maturity. And there are still others who feel this inclination more-or-less persistently from puberty onward.
It's important to recognize the existence of these varying tendencies, because, for one thing, one would want to shield a male with this kind of temperament, from being placed in morally challenging situation, a place of accentuated temptation and opportunity. Even if this man intends chastity, you don't put him in a submarine with a bunch of good-looking sailors, or make him a voice tutor for the Vienna Boys' Choir.