I would disagree with 'has to be comfortable to use' as that is often at odds with 'secure'. Some of the things I do to secure my system make infrequently done/high risk things quite uncomfortable to use. Not because I wanted to make it uncomfortable, but because that's what it took to get the level of security I desired.
[1] I would also argue that spending too much effort here before addressing other attack vectors first is rather silly. (i.e. web browser, network, minimizing usage of/isolating 3rd party binaries)
I also have to agree with you on the “one can make it secure” part, e.g. android builds on top of pretty standard linux tools to achieve its better security, namely selinux for a larger boundary and the most important: running different processes as different users! It is such a gaping security issue in typical DEs, as otherwise not even the very crude UNIX permission system can do anything meaningful (other than the relevant xckcd comic: the attacker can access all my files, my browser cache, etc, but at least can’t install a video driver)