Concerning the A/V vs experienced users:
I had a programmer come to me and be pissed that our barracuda firewall would block .exe files automatically. His point was that he was an experience software programmer, and that he needed to communicate to his co-workers some .exes files, as they were his tools for working. Now it isn't even my place in the company to take such decision as which files to block, but my answer was as follows :
''Have you ever done any kind of mistake in your life? Going from picking the wrong type of milk to slipping your finger on the mouse click, deleting the wrong file, mis-reading a text? If yes, then you understand why we can't allow anyone to risk the company getting infected as small as the risks may be.''
Yes, running without an A/V might not get you any viruses, running with an A/V may actually get you some (these are not magic gates either!!) but at the end of the day, a nice complete form of security will HELP prevent the risk of infection. No matter if these infections come from a simple mistake, an unexperienced user, a sister using your PC, or a late night slip up on the mousepad. Use both a trusted software and your brains, that should get you through.