That's a pretty high bar, I don't blame your friend at all for being skeptical.
Hard disagree. Total control of my computing environment would be to allow an application access to my documents, a space to save a configuration, perhaps my Videos folder or even certain files in that folder. Or conversely, not.
At the moment, none of the desktops give me the ability to set a level of trust for an application. I can't execute Dr. Robotniks Ring Run (or whatever the example was) and be able to specify what it can, or cannot access. There may be a request for permission at a system level access, but that could be explained away as usually is for iApps and Android when requesting some scary sounding permission groups.
And it also doesn't stop malware from accessing my documents. Sometimes my Mac asks if an application is allowed to access Documents, but it isn't consistent.
That's really the main point for me. Flatpak could also a lot of this, but Flatseal isn't the default, nor is it easy for users.
MacOS has a bunch of switches for access, but they are hidden away inside the settings, and they are not granular.
If it's not the default, and it's not easy then it may as well not be there for most people.
The switches default to off though, with a prompt on first attempt at accessing the protected resource.
The problem is that they're leaky like a sieve and the permission model and inheritance works is unclear (I once had the Terminal app ask me for permission - does it now mean anything I run from the terminal automatically inherits it - and so on).
Ultimately there needs to be trust at some point because nobody is realistically going to do a detailed security analysis of the source code of everything they install. We do this all the time as software developers; why do I trust that `pip install SQLAlchemy==2.0.45` isn't going to install a cryptominer on my system? It's certainly not because I've inspected the source code, it's because there's a web of trust in the ecosystem (well-known package, lots of downloads, if there were malware someone would have likely noticed before me).
> still running a random binary
Again "random" here is untrue, there's nothing random about it. You're running a binary which is published by the maintainers of some software. You're deciding how much you trust those maintainers (and their binary publishing processes, and whoever is hosting their binary).