I don't know the applicable US law, but there might be a difference between mandatory arbitration and civil law suits on one hand, and criminal law on the other.
It couldn't be that you sign something with a company, and that contract also means police can't do shit about shit.
I guess racism is part of criminal law? And besides, it is really easy to not be racist.
There is more than on reason folks do mandatory arbitration agreements - I'm not entirely sure this is the main one. Mandatory arbitration keeps such things out of the public record and often silences the accuser.