I think the big question that I have not seen discussed anywhere is whether Linux supports muti-user systems or not.
Well, you might say of it does, it always has.
If you see computing as a technical activity like it was 1970 - 1990, I agree.
But if you that you have your private life in the machine, money and whatever. I'd say no. A user should not see who else has processes running and what they are. A user should not see who has a home directory.
Not a relevant issue you say, we all run de-facto single user PCs. Yes, we do, but I think only LWN readers and the like should. Others better use something like LTSP or ChromiumOS, some kind of lightweight client solution. Currently Linux cannot be used straightforward as the server for such a computing model. I'd assume patches required to do so would also deemed "entirely insane".
If you explictly said we support only single user machines I'd agree that many of the "security issues" are non-issues. Loss of privacy = sniffing your own data. Denial of service = turning your machine off. But I don't think anybody has said the Linux should never support building servers for multi-user systems.
Or are we just hitting the limits of one size fits all? What fits a cell phone or a wireless router, can it fit a multi-user server? And because the limits have not been agreed, people fight what is reasonable and unconditionally insane.