I just think he has some mild social anxiety/awkwardness.
Transporter phobia is something I can understand, and Barclay's not alone in that. McCoy and Pulaski hated the thing too.
And if holodecks actually existed, I'm sure holoaddiction would be a major, major social problem, but not indicative of greater mental illness on the addict.
I think Barclay's biggest problem was that he was a very intelligent, but otherwise average guy stuck on a ship full of near-perfect people.