It probably has more than one etiology.
In some cases it appears to be hereditary, at least in part, and is a disease as certainly as any other hereditary disease, e.g. hemophilia, Down's syndrome, sickle cell disease, et al.
In some cases, it results from trauma, e.g. sexual molestation in childhood, and is a disease as certainly as any resulting from stress, e.g. PTSD (post-traumatic stress disorder), hysterical paralysis, et al.
Another etiology is habitual homosexual activity, especially if starting at an early age, becoming habit and ultimately addiction.
Homosexuality is a reaction to injury, resulting in disfunction of the reproductive system, and is thus, by definition, is a disease.
Reclassification, wishful thinking, or anything else will not change this.
Homosexual activity appears to be different from homosexuality. It appears that most people can engage in homosexual activity under certain circumstances. It might be nature's way of releasing powerful sexual tension under such circumstances.
Can’t be hereditary. There is no homosexual gene. It is a taught learned behavior or else it would not have to be “taught” to young kids in the school system or anywhere else.