This is the artificial design of Unix-like operating systems like GNU/Linux. Mounting of file system is a privileged operation in Unix-like operating systems. The system call for mounting requires root priveleges.

The binary you invoke to mount a sshfs file system is not setuid root. But it calls a function from libfuse which in turn invokes fusermount which is setuid root. Remove the s-bit from /bin/fusermount and unprivileged users will no longer be able to mount any file system that uses libfuse.

There are different ways to allow unprivileged users to mount a file system. They all come with some restrictions to avoid security issues.

• The traditionall way is to require an entry in fstab. That is what davfs2 supports.

• fuse additionally allows users to mount a file system if they own the mount point and it will restrict access to this file system to the mounting user only. root can influence this restriction via /etc/fuse.conf.

• Most desktop environments have some component that allows unpriveleged usrs restricted mounts. But I don't know much about this.

I am considering to add an option like fuse (restricted to mount points in the user's home directory). But I don't consider this a high priority issue.