You can give a loaded AK47 to a chimp as well, doesnt mean you wont get shot..
Considering you can be infected by worms without having to actually action anything on your part, and if you use the internet for things like banking, then it would be foolish to not have some form of protection when it is so cheap to do so.
I used to collect virus's, had over 3,000 of them back when i was into coding and ran a few on my PC to experiment, I probably have better understanding than most on how virus's work and spread, and still, i think it is rather foolish not to have an antivirus, even though i dont think i would ever accidently run one.
