The way I see it, paranoia is like an exaggerated form of doubt and mistrust. I don't know whether or not a dose of it is healthy but it's natural with every human. That speck of doubt will always be there. It's instinctive.
The danger lies in when it becomes too much. We begin to see lies where truth is and consequently lose good friendships. Usually, I try to see the good in people to start with...later on, the not-so-good part will show up in their character some how. 🙂
I want to do this, see good instead of bad in people but most days I can't