There's a problem with loading the home directory as a loopback block device from roaming USB disks - untrusted filesystems aren't safe to mount.

From https://lwn.net/Articles/755593/ "Unprivileged filesystem mounts, 2018 edition":

> There's little we can do to prevent people from exploiting flaws in the filesystem's on-disk format. No filesystem has robust, exhaustive verification of all it's metadata, nor is that something we can really check at runtime due to the complexity and overhead of runtime checking. [...] "Go run your filesystem in userspace with fuse if you want stronger security guarantees."

But the same topic is also discussed in many similar articles, e.g. more recently regarding the likeliness of opening new bugs for everyone using automount since the new EROFS filesystem has been merged into the mainline kernel.