I think homosexuality is a mild mental disorder.
Why?
High rates of co-morbidity with major depressive disorder.
Symptoms are comparable with disorders such as pica disorder, in which a subject desires to fulfill hunger needs with non-food items. (e.g. rocks, sticks, coins)
Per capita, homosexual cases of pedophilia are far more common than heterosexual cases.
High correlation with childhood sexual abuse, suggesting a possible etiology.
Common arguments which fall somewhat flat.
It's natural because animals do it.
This is true, there are animals which partake in homosexual relationships. However, animals are also capable of developing some of the same psychological conditions as humans. They've even been used in the study of human psychology. (e.g. Learned helplessness was tested in dogs, Ivan Pavlov's conditioning experiments)
Consenting adults make it okay
Most people would say that those whom are mentally ill can not consent. I don't think it should be illegal, but it should not be encouraged.
Almost all STDs are more common in homosexual (male) relationships, than in heterosexual relationships, and as mentioned previously, it has high rates of co-morbidity with other doubtlessly harmful disorders. Furthermore, homosexuals are more prone to other risky behaviors such as alcoholism, and drug use.
The classic Kinsey argument. Commonality does not mean something ceases to be a disease, or disorder. Eating disorders are very common in the US, and kill more people than any other mental disorder. (mainly anorexia) The logic, also doesn't apply outside of psychology, and into the rest of the medical community. If 90% of the population were to contract the common cold, it would not cease to be a disease.
