Re: This seems a very level-headed and straight forward discussion
Well additional security boundaries are a good thing by themselves, but experience has shown that those boundaries either have holes in them, or are irrelevant.
One example is ChromeOS which tries really hard to prevent you from getting to the kernel... which is completely irrelevant as you are only running a browser. Crack the browser and you are exactly where you want to be.
Same goes for Android where Malware can just ask the user to have access to all valuable data.
The basic problem is that you cannot contain malware. Once you have malware on your system, your system is compromised. All you can do is reduce your attack surface and make it easier to clean your system.