No. If the OS is locked down so only MS-signed applications can run, it is impossible to run software that can detect malware that has been approved by MS. It is also impossible to run software that can remove such malware.
If the OS makes it impossible to detect or remove malware, it is less secure than OS that do allow detection and removal of malware. This is not FUD.
What should happen, is that MS should be held strict liable for any illegal acts which their restrictions helps to propagate. Held under vicarious liability by non-US markets (so they can't get immunity by the US government), MS shareholders would demand the elimination of the restrictions in favor of less legal risk for the company.
Second, I haven't seen your argument made for iOS and Chromebooks which are much more locked down than Windows 8. Though one could argue that Chromebook doesn't need to have malware since everything is helpfully uploaded to the cloud.
It might had been worth mentioned, I am not the first person to talk about liability issues regarding lockdown. I first heard it in a talk that described the iPhone.