Hmmmm, I have known potheads to be a lot of things, but paranoid is not one of them. And certainly if it were actually true that pot causes paranoia it would have been incorporated in the pot smoking subculture, but just the opposite is the case, instead of having a reputation of being paranoid they have a reputation of being mellow and apathetic.
This study seems like complete garbage.
It's biggest danger is that it makes you lazy
http://www.youtube.com/watch?v=V2FZgErvNTE
Hmmmm, I have known potheads to be a lot of things, but paranoid is not one of them.
Unfortunately, neuroscience isnt based around your interpretation of how your friendship circle operates. Speak to a neuroscientist and get back to me.