ADHD is the classic example of this. Were I school age today I would almost certainly have been given the dual badges of ADHD and aspergers - my brother, who is seven years my junior, is labelled as both. Me, I'm just eccentric.
Why this bothers me is the outcome it can lead to. Having a "reason" for you being as you are leads to self-justification, to complacency at one's station in life. In his case he's medicated and in the eighth year of an undergraduate degree. I finished my masters in two years and founded a startup two years later as I am incapable of sitting still. I like being an undiagnosed creature, as I've ended up finding something that suits those traits in me, rather than suffering from them.
I know this is anecdotal, and this really isn't done diatribe against mental healthcare - plenty genuinely need it - but I worry that too many engage in that funnel out of some misdirected need to conform, and end up losing part of what and who they are.