Remember that most windows antivirus (except perhaps Microsoft's own) patches into the operating system somewhat similar to malware itself to do all the things

Remember that most windows antivirus (except perhaps Microsoft's own) patches into the operating system somewhat similar to malware itself to do all the things it does. Malware programs patching the same parts of the OS are likely to trip over each other. Such a combination would be highly unstable, not to speak of incredible slow.