It really is up to opinion, i think the word natural is opinionated, whether you want it to be all inclusive or bounded. In the end i think its just political correctness not wanting to hurt gay peoples feelings. There is something that is not right with homosexuality(meaning the brain chemistry somehow got messed up in some way at birth), but i dont think its the homosexuals fault, much like if you have ADHD, albino, minor gigantism, dwarfism.
What word would you use to describe homosexuals, albinos, midgets?.... its really hard to not come up with something that doesn't sound 'mean'. Unnatural is just a word to describe people with attributes that differ from the regular homo-sapien make-up in which has the most efficient functionality as a healthy human being.
Homosexuality is a dysfunction because it decreases the sex drive to the opposite sex, which results in decrease chance in reproduction.... which is the only meaning of life as we know it according to biology, to reproduce.
I believe most of us have some sort of dysfunction caused by many factors, but i think those are no less 'unnatural'.