Is it? Did "all lives matter" help prevent police brutality? Or was it an attempt at whataboutism so you don't have to do anything?

There wasn't really an all lives matter on the same sense as the black lives matter movement.

Plus there's 'all lives matter' as in the proponent doesn't want to do anything, and 'all lives matter' as in police brutality is bad no matter who it's aimed at, and should be stopped completely.

The latter more closely mirrors the parents example.

Further I would say your example is flawed. BLM assumed a level of racism that I don't think there is. This isn't a case of KKK members wanting to get the <racist slur>s out of the country and back where 'they belong' it's more an issue of laziness and profiling. That isn't to say it isn't racism, but just talking about racism allows police that aren't KKK members to tell themselves they aren't the problem. Focussing on the issues of laziness etc means they do actually need to face up to the issues.

The same thing with genital mutilation, this isn't simply a case of something that happens to girls in a far away land, this is happening to kids right now in the west. Focusing on FGM kind of misses the point.