Installing apps without being root isn't too simple ... but more important only root can bind "input" ports, so no app can bind to a port and listen for an input connection whithout having root privileges (at least for binding time) AND only root (or a good cracker
) can give it root privileges.
So simplifing:
Only root "installed" daemons can bind "input" ports!
Just for info there are systems configured in special ways that can permit to non-root to bind ports using capabilities ... but it isn't your case.