That sort of thing leaves an indelible mark.
It's worked out as Clinton vs. Sanders, or more accurately some Sanders supporters vs. non-Sanders supporters (some support O'Malley, some Clinton, and a good number are undecided) because of how members of color on this site have been treated. It is not a stereotype. It is their experience. It is also something that has been painful for me to watch, even though I am white. I can't begin to imagine what was like for African Americans, some of whom actively participating here as Sanders supporters before the backlash to the Black Lives Matter events.
I appreciate the unity today surrounding Clinton's testimony, and I respect your and anyone else's right to choose whatever candidate you like for the Democratic nomination. But the threads I saw following the two events where Black Lives Matter interrupted Sanders, in which far too many participated in perverse conspiracies created to discredit black activists fighting to save the lives of Americans, are not something anyone can or in my view should forget. Some want to pretend it never happened, or that it was somehow a creation of the Clinton campaign, but many of us remember with great clarity exactly what transpired. Some chose to show us who they are, and that cannot be unseen.
You can have whatever theoretical position about race and class that you want, but that does not substitute for the experience of being black or another person of color. I submit that the answer lies in listening, and that means being subject to conversations that may make us, as white people, uncomfortable. That is not "divisive." It is part of being a socially conscious member of a diverse society that continues to be racked by racism.