Condemning incidences of police brutality (which Sanders has done, and has a better record than most candidates on) does not make a concrete policy proposal to solve the issue, nor does talking about past support for civil rights.
I think this is the most important issue here and is the key to understanding why this portion of BLM chose to take the stage. It's not because he's white and they're against white people, it's because Sanders is likely the only candidate who would be willing to listen and put together a real plan to address the issues which made BLM happen. He needs to take this seriously and treat it the same as he has economic issues.
However, looking at the broader picture, is interrupting a rally the best way to make the candidates talk about the issues pertaining to black lives, or is it deterring people away? If this type of action does lead to real change and prompts Sanders to push social issues more in his campaign, then I'm all for it, but the consensus seems to be that it's hindering them more then helping.
