It's more what you don't know (Score 1)

than what you do know. I consider the anti-virus software I run on my Macbook Pro to be there more so that I don't have to keep constantly up to date with whatever might be happening in the world of security/vxers. Put it this way - you can go out in your car without a spare tyre or a can of tyre-weld or whatever. Yes, you're more than likely going to get to your destination - but there's an element of risk, just like running OSX without anti-virus software. Theoretically, you're not likely to get a virus in the current environment. That's not to say it's a dead cert, though.