There are people in the world who don't live by the credo "an injury to one is an injury to all". Some of those people benefit materially from their willingness to separate themselves from their communities. White folks are less likely to be targeted by cops than black folks if and when they aren't engaged in consequential direct action to threaten capitalist power. White folks are unlikely to be tackled by ICE as long as they keep a low profile, which might be easy for some white folks in particular if they choose to exclude themselves from their communities for their own material benefit. I think, personally, that there are huge social and emotional costs to this kind of behavior, but on a superficial level, it happens.

On the other hand, some leftist spaces focus on some element of identity, be that gender, race, sexuality, or religion to the exclusion of what unites us, which is our position in the class hierarchy. 

Our shared struggle is against the capitalists, and while the capitalists may use race as a tool to divide the working class, the tactics that the working class uses are the tactics of workers.

Yes, the capitalists are using race as a tool, and that means that white folks who don't already recognize that we share a struggle have a little more time to pretend that the propaganda telling everyone that MLK was purely peaceful and he won concessions from the ruling class by just making a bunch of people realize they were wrong by being unerringly peaceful.