I am not saying anti-virus programs are viruses. People need anti-viruses to stop spread of malicious software only because Windows is inadequate at protecting itself. Malicious softwares work by exploiting software vulnerabilities (aka bugs). In a well-designed OS, no anti-virus is needed. Take, for example, Mac OS X or Linux. There was once a proof-of-concept virus written for Linux a few years ago, just to prove that Linux security is not perfect, and it was recognized as a bug in Linux, and was fixed by the Linux people (where Microsoft would irresponsibly recommend users to install an anti-virus to combat that). IMHO, that is the level of security an OS should seek to achieve. Also worth noting that Windows is the only OS out of hundreds currently in use today that requires an anti-virus for normal operation.
Well, no, not all... Anti-virus software stop spread of malicious software, for one. That has nothing to do with the operating system.
Many security companies add extra security to Windows, not fix bugs... They aren't bugs, it's more like it's missing security features.
But then, if they tried to add it, they would probably find EU breathing down their necks.