Yes, I would prefer all Mac owners to be a bit more responsible and install an AV program.
While I/they know they are basically immune to Windows Viruses and other nasties, they can become carriers or unwitting sources. Mac user, using an AV program, can offer downstream protection, that is to say, their AV program is also scanning for Windows' nasties.
Mac antivirus software is in short supply and the options for free Mac virus scanners is even more limited. Still, there are a couple of free Mac antivirus software available. For details, see:
Free Antivirus Software.
Clam is also a favourite with Linux users.
All the major pay-for AV vendors do a Mac version.