To explain why the CS, NHS, public sector etc. have so many diversity groups.
The CS was created around c1850, NHS created in 1948. They predate any type of equality legislation as we know it.
The CS is required to deliver the business of the government of the day. The expectation is it not only acts lawfully but also leads the way in employment terms. CS Departments know ETs will hold them to a higher standard of behaviour as an employer and hate it if Case Law (EATs) is created because they got the law it wrong.
Departments need a way to effectively consult employees on new and revised policies, some are required as part of legislative changes. The PSED applies a duty to consider protected characteristics (pc). So in addition to TUs, Diversity Groups were set up to allow the business (HR ) to consult with employees who had relevant personal experience to ensure policies and procedures were inclusive and where possible removed barriers.
A good example is Fire Evacuation procedures in a tower block. You need to think about deaf employees not hearing an alarm, wheel chair users, employees with mobility and sight impairments, pregnant women and potentially short term impairments like a broken leg etc. who may not be able to walk down 14 flights of stairs. Diversity Groups can add a lot of value to the development of a policy.
The problem is the number of groups has expanded to make it unmanageable and time consuming. The Gender Reassignment pc has also disproportionally absorbed time and resource.