Imagine you have a disk full of your precious data that you want to mount to a new Ubuntu Linux system and add user to match the existing home directory.
# adduser user Adding user `user' ... Adding new group `user' (1000) ... Adding new user `user' (1000) with group `user' ... Creating home directory `/home/user' ... Stopped: Couldn't create home directory `/home/user': File exists. Removing directory `/home/user' ... Removing user `user' ... Removing group `user' ... groupdel: group 'user' does not exist adduser: `groupdel user' returned error code 6. Exiting.
Now you can say your all precious data goodbye. No questions asked. Core Linux utility
adduser just found your existing data and erased them without even asking. The years is 2021 (30 years since Linux was created).
This is why for over 15 years I am only working with BSD Operating Systems    . Its Open-Source with long-term maintenance and self-compatibility in mind. BSD license is even more liberal than GPL for your products . You should try BSD too :-)