so many rogue spyware programs

I always give users the benefit of the doubt when it comes to judging those who have been infected, but everyday I find more and more people with rogue programs. I am sure they are aware that they have antivirus on their PCs, most likely installed by their system's engineer, so why would they allow other program on their PC, and when they look at it they go: 'ohh, well it told me there was something wrong with my computer, I thought it was helping' it just makes me grind my gears...