Unix, and everything modeled on it assumes competent users running applications they wrote for their own use. Anything that follows this model can't ever be made secure without rendering it useless well before then.
Capability Based OSs can be just as easy to use as Unix, except for the core assumption that code is to be trusted. When I say capabilities, I mean fine grained ones, like access to a file, which could then even be filtered down to access to part of a file, or read-only, etc.. then passed on to other tasks that require it. It makes permission composable, like being able to make $16.23 from exact change, instead of handing your wallet to the cashier and hoping for the best.
Until Capability Based Security becomes the norm, no nodes on the internet are safe, and it will always be an excuse to clamp down on freedoms. If we are to have freedom, we have to migrate to Capability Based Systems, and then continue on to win the war for general purpose computation, which most people don't even realize is already in play.
If you're old enough, remember shareware and dual floppy drive PCs? You could try out anything, and not worry a bit, because you didn't risk everything to the code you picked up for $2 on a shareware disk, you could always return to a known state. Capability Based Security makes that possible, even with mobile code on the internet.