There are now almost 100 million devices connected at least some of the time to the Internet running one version or another of Mac OS. This includes tens of millions of Macs as well as iPhones, iPod Touches and the new iPads. Few if any of them ever employ security software beyond that built into the Unix-based Mac OS. Nevertheless, it's virtually unheard of for malware to be effective in the wild and there have been essentially no viruses propagated from Mac to Mac. This the polar opposite of the Windows world which to us seems to be a virus and malware nightmare.
Beyond that, it's just a personal preference issue.
“seems”
Just that, seems. Those of us in the security world know better.