Run a *NIX machine, no such thing as any realistic virus threat in that world...
Or run Windows machine solely for trading - No P2P, no browsing, no IM, no external media ever read by computer except 100% trusted (such as legal copy of software) behind a decent firewall, all recent patches installed and no AV really needed then too.
As for "usual" machine: backup, backup and again, backup...
Most important content of computer these days is data, not some piece of crap code aka OS.
So, backup your data regularly and don't care much about "bug which can destroy OS". Reinstalling OS and software from scratch is like a day of work in worst case, loss of important data can be equal to loss of years of work.
Still, I think it's wrong statement that chance of catching a virus is lower than chance of destructive A/V software bug.
Experienced many viruses in my life on many computers, but never had any crashed by A/V software itself.