As long as you avoid downloading torrents and using Java, you don't need an antivirus on the Mac.
The one big infection on Mac was a Trojan botnet that came via pirated software. Java has some problems as well and should be avoided in the browser.
I mean, I have barely ever used antivirus on Windows without having an issue. (And yes, I have scanned my drive so I know I was clean)
The unpopular fact is that viruses are not what they used to be. Antivirus and security has been marketed into everybody's brain, but the reality is something different: almost all malware these days is either botnet or money related, and most comes because people download crap they shouldn't. (A small number comes from browser plugin holes).
And almost all spyware is ignored by antivirus software, which will let you install nonsense like Conduit search without stopping you. Even malwarebytes and superantispyware won't stop you from installing much of it.
Over the next few months we will be running some pretty shocking articles related to malware. Reality is not what you think it is.