Bernie needs some help in creating a credible foreign policy that puts America on a path to dealing with the excesses, abuses and failed policy of previous administrations. His foreign policy also has to support his economic goals. It seems unlikely that the US can continue to support the enormous costs of military engagements, the ongoing costs of sustaining the veterans of those engagements, the costs of nation building in the countries where the US has destroyed infrastructure and created political chaos as well as the costs of an oversized global military footprint to maintain US hegemony at the same time as enormous investments are needed at home to rebuild infrastructure and provide for the needs of citizens.
If you are one of the millions of people who are tired of the endless wars of choice, the war tactics and equipment that seem to keep showing up in the hands of domestic police, the encroachment of the surveillance state on virtually everybody - among other things, then getting Bernie to commit to correcting those wrongs is the right thing to do.
Politicians never listen better than when they want something from you. This is the time to make your favorite politician a better representative of your interests.
It will have the benefit of making Bernie a better candidate. Whatever you think of #BlackLivesMatter, they engaged Bernie - and his platform, his performance on the stump and his currently proposed legislation are better for the challenge.