I don't have a good answer for you, but I think it's a damn good question and something which irritates the hell out of me.
The definition of 'paranoia': Paranoia is an unfounded or exaggerated distrust of others, sometimes reaching delusional proportions. Paranoid individuals constantly suspect the motives of those around them, and believe that certain individuals, or people in general, are "out to get them".
Source:
http://medical-dictionary.thefreedic...y.com/paranoia
Now, I don't know any mental health professional/team which really goes ahead and disproves a person's 'paranoid' theories before diagnosing or medicating them with/for a mental illness.
Some people may have good reason to be suspicious of those around them. Even concerns which sound like 'bizarre delusions' could be based very much in reality... can we really trust the government? My frustration is not so much that people don't believe my beliefs - that's their prerogative, but that they are arrogant enough to tell me that it absolutely can't be true (whilst telling me to strive for an element of doubt!) and then force their meds on me.
Okay so that turned into a bit of a personal rant, which I wish I could have put more articulately (but I can't, so) - basically, I agree it's a grave concern.