If homosexuality was a mental disorder according to the dmiv in the past how do you know current mental disorders won't be normal in the future?

You don't: "fashions" change and so does thinking about the variations in human behavior. Some conditions became included as subtypes of other and some subtypes became common enough to stand alone. It's only the way experts talk to each other about the problems people come to them with. The one you mention is clear as to how it can happen. Don't let it worry you too much. What is, is. What we call it, well?

Knowledge changes.: Good science replaces false ideas ; superstitions with more accurate understanding. We know the earth is not flat ; epilepsy, leprosy ; homosexuality are not punishments for sin. But science isn't perfect ; is continually being updated. Mental disorders are not yet well understood. Some current dsm diagnoses are controversial ; will change with time. Profit motives can distort science.

Point O's : Exactly! In fact, we can count on this. I am certain some conditions currently identified in DSM 5 (5.0) will be dropped or changed. Even DSM 5's authors expect this. And they expect revisions periodically. Coming soon: DSM 5.1! For background article, see http://ow.ly/3uXdRG