And they still work precisely because the user can do that.
> For decades we've been continually looking for better ways of isolating local apps, while also rejecting centralized control.
The main issue is that there is so little real benefit in it. It's possible to isolate e.g. LibreOffice so that it can't access anything it shouldn't, but in general the authors can be trusted not to be doing anything nefarious to begin with, so what you're really doing is limiting the damage in the event of compromise. In which case you're still pretty screwed, because it inherently needs access to your documents, so the focus has not surprisingly been on preventing compromise rather than mitigating after the fact.
> We keep looking, while centralization keeps ratcheting.
The motivations behind the rise in centralization are authoritarian and pecuniary rather than any legitimate security concern. Trying to prevent it by finding alternative ways to improve security is like trying to repeal the DMCA anti-circumvention rules by finding alternative ways to reduce piracy. They'll never be satisfied because their motivations aren't the stated ones.
It's a dream. Kept alive by a very diligent community, but let's not kid ourselves that it's a very strong assumption.
> In which case you're still pretty screwed, because it inherently needs access to your documents
Access to the specific document you presently want to edit (say through an OS-provided file select dialog or equivalent cli) is much different than unfettered access to all of your files.
> The motivations behind the rise in centralization are authoritarian and pecuniary rather than any legitimate security concern
People do choose say Apple products precisely because of the curated Disneyland App store. Centralizers certainly have their selfish motives, but people are driven into their arms looking for safety. Browsers are used for software distribution precisely because they're a sandbox - there's much less fear of the unknown than running a random exe.
This is one thing I like about Android. You can avoid requesting file permissions for your app by using native intents for file access. I think its the same for other stuff, like email. As much as I loathe Googles control over Android, I think this is a good thing.
And you can install an anti-paywall extension in Firefox.
The moment you concede the Linux "well you can work around it" argument is the moment you have to stop arguing on pure absolute principle and start arguing about practicality and the relative difficulty of workarounds.
The difference is that Linux repositories are less noteworthy to attack, have a more distributed culture not ruled by capitulating lawyers, and can actually jurisdiction shop.
The ultimate problem is a lack of a cross-software security model of the OSs, Linux included. User-based isolation is cool and all, but orthogonal to the modern world [0]. For decades we've been continually looking for better ways of isolating local apps, while also rejecting centralized control. We keep looking, while centralization keeps ratcheting.
I'm still hopeful that a well done capability (handle-based) system would go a long way, but not fully solve it. Unfortunately that means shedding off POSIX/LSB rather than duplicating the entire monolithic OS environment for every security context.
[0] Where say even a local LAN IP address is security-critical information!