I suspect most people don't really mean that when they say it.
It makes no sense for pro-black people to complain about anti-FBA/anti-black behavior being called out.
The callouts should be divisive, to divide ourselves from the bullshit that will betray pro-black/pro-FBA causes.
In the case of racist(immigrants), they already divided themselves from black Americans, or black people, long ago.
And we have no obligation to suffer their bullshit, regardless of their skin color or nationality.
When applied in this manner, being divisive can be a constructive move that benefits correcting injustices.