When this was added as an option it was defaulted to checked for all courses and new courses without an option in admin settings. Students can make groups without the teacher knowing, as the teacher didn't enable this setting. This is a horrible idea for K-12 instances of Canvas. I'm not a big fan of the option even existing but certainly not defaulted to checked.
There are several features where you can select to have it checked by default and even lock your selection for the courses made below that account level such as; restricting student viewing of a course before start date, after start date, and more. This seems a perfect instance where it should be handled in the same manner.
At least having it default to unchecked would be better as it would be in the teachers' hands to enable if they wanted to use it (or programmers' hands to hide it if an institution didn't want it at all).
Added to Theme
Bring account settings inheritance into parity with feature options and roles or permissions Theme Status: Identified