Buy mac and don't worry 
Was just going to post the same.... 
That'll be why you can't buy anti virus for Macs then..... 
Well... more fool the knobs that buy it, because its not necessary. Ive had macs for 5/6 years and looked at plenty of gentlemans literature, and not got a single virus. 
Macs are not impervious to infection, over the past 5years 2 or 3 viruses Vhave been released that have caught people by surprise.
You may think 2 or 3?? That's not a lot, it is when you have no protection from them.
You can get anti virus programs for mac.