I guess the problem is in how we define legitimate. Science can take a legitimate stab at what causes homosexual desire. But science is being dishonest to deny the anatomy of a person in the process of analyzing the data. A woman with a womb, ovaries, etc. is obviously not born homsexual. She may have sexual thoughts and desires towards other women, but to interpret those desires as normal is "science" ignoring science.
Not sure exactly what you said. However, you are making some assertions: 1) someone is not born homosexual - while this is true to the extent that people are not born expressing a sexual preference (either way), it contradicts the current data on genetic and environmental exposures in utero in determining to some extent sexual preference. This is not to deny environment or choice, of course; but this is not to say what I think you were trying to say. 2) science decides what is "normal" - this assertion is also questionable; a good scientist does not use the term "normal" as I think you used it.