One day people are complaing because MS is monopolizing the market, and Bill is accused of supplying sortware free (IE) to drive the conpetition out of buisness (Netscape)...and now they will complain about having to pay for add on programs to protect their PCs.
The problem is that MS is wanting to charge to solve a problem that they are at least partially responsible for. The massive holes in IE, Outlook, OE, and various core parts of the OS are what allow some of the spyware/malware in. Charging to remove those is unethical. Selling a defective product and then charging to fix the result of those defects is also illegal in most places.
That said, not all spyware/malware exploits bugs. A good bit of it is from people idiotically clicking "OK" to everything, and slimy companies putting crap in their EULAs that gives them the "right" to screw over the user. In that situation, I have no problem with MS, or anyone else, marketing a tool to help undo the problem. If you feel you can charge money for the service, go for it. More power to you.
The problem here is that the two categories overlap pretty heavily, and MS has a pretty lousy security record overall.