What I mean by "a little paranoia (but not overly so)" is that paranoia can be "mild", and by definition doesn't always have to involve delusions or extreme irrational anxiety. I think a mild paranoia is "justified" in the sense that you can't always trust people or trust that you won't be let go from your job. A lot of people are mildly paranoid of losing their job IMO, especially given this poor economy. Plus, people (bosses, co-workers) are unpredictable. When it comes down to it, we live in a dog-eat-dog world.

Now personally, I think it's pretty rare to work in a safe, secure environment these days. I also don't think anyone is ever treated well and fairly. Life isn't fair, jobs aren't fair, nothing is fair. There will always be people who get more than they deserve and people who get less than they deserve. So in theory, yes, you would perform best in a safe, secure environment where you're treated fairly, but unfortunately, that sort of environment is almost unheard of IMO. I am motivated to do my best because I feel that nothing is secure and I don't want to lose my job. And I know that no matter where I go (job wise), employees aren't going to be treated fairly.

But yes, I agree that moderate to severe paranoia to the point you're delusional would definitely affect job performance.