lowest common denominator
...a math term from grade school.
...a term metaphorically used to denote that left to their own devices, many persons within systems and groups allow the average quality of that produced jointly, to drift to the lowest standard held by any member of the group.
...this saddens many people, and leads to attempts to organize and then work towards higher quality standards. This in turn leads to exclusion ot those members in the system or group who cannot / will not support working to uphold higher standards.