With the right spin, this is what I believed from the beginning about Microsoft Security Essentials. If the company can't even write a decent, secure operating system to begin with, why should we trust them to write decent dedicated antivirus software? What reason could we as a population of computer users have for having any confidence in this product? Of course it should be a relatively terrible at protecting a user's computer from viruses, because it comes from the same company who has that sort of track record with viruses in the OS to begin with (that is, the same reason why antivirus software is pushed onto users in the first place).
To believe that Microsoft Security Essentials is any good at what it is ostensibly meant to do is to believe that Microsoft is good at detecting and clearing viruses from users' systems, but to believe this is to hold a contradiction to every observation made of various versions of the Windows operating system.