What I mean is that it should ignore permissions on external ext4 by default in Desktops.

There's no concept of "external". What would it be, "USB" or anything mounted under /mnt or /media? What if it's the root OS drive of another computer you're trying to fix connected through a USB-SATA adapter? Should any program running with minimized privileges get to overwrite even root files in that OS drive?

I think that it's a pretty good heuristic that if permissions exist in the filesystem, they matter and shouldn't be ignored.