The argument is that creating classes and lessons that explicitly point out and "otherise" a race will cause any groups being told about this to discriminate and hold biases against said race more often not less often.
The main issues of race today, outside of the issues of continued poverty and fundamentally flawed laws concerning safety nets, public spending, and so on, is the fact that people make thousands of subconscious judgments every day based on race. Nobody is "racist" anymore, but everyone is a little more willing to believe a black person is a criminal based on what they have learned. Everyone is a little more willing to judge a job applicant as being less ready if the applicant has a black sounding name.
People behave based on the environment they are in. If the ultimate goal is to reduce the above state of mind, to reduce those subconscious biases, then the methods in use for the last 50 years are not going to succeed, and will in fact backfire.
The argument is that future policy should focus not on education about the differences or hardships that black people face, but instead to focus on "integrating" all races and focusing on making all people view one another, subconsciously, as peers. To focus these students to think as a united group, rather than as multiple groups.
It isn't that teaching people about the things other races face is a bad thing, it's just that doing so will end up in the result that black people will face more discrimination and more judgment from the general population as a result. Even as we all accept black people accept more hardships, we will still continue to look at them as if they are different, as if they are a group not a part of the national whole.
The people being made aware of racial disparities in a class aren't going to ever be part of the solution to fixing those issues. While it is a noble goal, it will ultimately fail.
It is the people who have zero issue treating the black person next to them as they would any other person, and learning firsthand what that person faces which will ultimately inspire the empathy and passion needed to drive forward progress of race in the US. Lessons about micro-aggressions will only make tensions worse and subconscious biases stronger.