Viruses don't take up HUGE wads of disk space. Viruses don't need 4meg of ram to run. Viruses do something. Viruses don't have major bugs. Viruses don't have three different sets of documentation that is all mixed up and wrong.
Viruses arn't on every computer.
Viruses don't have stupid wizards. Viruses when installing themselves don't try to send private info about your computer over the phone lines to microstoned-net. Viruses install themselves. Viruses don't try to push out all compitition. They just try to do their job.