Thinking about it I came to realize that there is a much deeper cultural problem: it became the norm for users to run lots of opaque untrusted code on their computers. Every application is a threat, as it represents interests of the vendor rather than the user, and this can not be solved just by isolating UIs (the line of death) and code (sandboxing), we must reconsider the models of software distribution that we use. Maybe the Web should not at all be used as an application platform and instead focus on content and give more control of its representation to user agents.
And there actually is a software distribution model that gives grounds to trust — the one used by GNU/Linux distributions where software is not pushed to the users by vendors directly, but reviewed, built from source and packaged by distribution maintainers who represent the interests of their users. And of course, for the maintainers to be trusted, their work must be maximally transparent and verifiable. Some distributions, like GNU Guix, managed to advance this model really well, while others are unfortunately now going in the opposite direction by adopting things like Flatpak and Snap.