Its a pet peeve of mine that the GNU/Linux world is 99% of the way to an incredible degree of security but distros are totally disinterested in going the last mile, often because its a lot of boring work.
Mandatory Access Control should have been game changing in the security sphere, especially in the era of cgroups. Fine grained permissions controls in the kernel and filesystem would stomp out almost all potential malware vectors - both exploited software and injected binaries. GUI desktops could have provided UI to prompt users for unknown programs trying to access specific things and then send reports upstream of programs allowed for review. It would practically be a self-building database of program file access if done right.
But that isn't the only avenue to it. You could pressure upstream to include discriptor files in git repos of a standardized format of file access for each binary that can be used to generate selinux / apparmor / tomoyo rules. You could do it the really hard way and just have a sprint to surface test every program in official repos and generate such files yourself. Programs should almost never be accessing anything outside their XDG conf file and data dir - they should be linking libraries to provide access to other stuff (input, gui, etc) and file access should go through the system wide file picker.
As it is right now though pretty much every executed binary on most Linux systems is allowed to do whatever it wants that it has user access privilege to. Especially because most maintainers don't want to have to bother with the complaints of malcontent software breaking constantly trying to read arbitrary files. The Apparmor profiles of SUSE / Ubuntu or SELinux of Fedora are largely written for a few specific programs, usually web browsers and file sharing daemons, rather than be comprehensive. Its such a shame that all the technologies exist and are in place to make this work (even Arch has Apparmor support in its official repos now!) but there is no willpower / capital / interest in going the last step and trying to be all encompassing in your MAC profile and then lock down unknown programs appropriately. Android pretty much does this already, its a shame desktop Linux totally skipped over this avenue towards secure desktops.
There is of course an argument that if you lock down programs with network access then thats all you need to secure your desktop but that position falters in the face of arbitrary programs being run at random that can include network access. The goal should be a default restricted profile - one where arbitrary binaries cannot do whatever they want to your system, in the context of having a comprehensive profile database of software being used that covers 99% of real world program usage and thus doesn't impose a sizable UX burden of constant usage prompts for common applications.