WASHINGTON — Leading up to his meeting with the Black Lives Matter group Campaign Zero at the Frederick Douglass House in September, Democratic presidential candidate Bernie Sanders steeled himself for an argument.

He’d only previously come face-to-face with Black Lives Matter protesters who wanted to interrupt him. But over the course of the meeting, the activists spoke authoritatively on policy recommendations to curb racial disparities in the criminal justice system, while Sanders impressed by synthesizing their talking points on police militarization, community empowerment, and systematic oppression.

The activists brought up one issue, however, that Sanders hadn’t considered: creating pathways for black Americans to take part in the emerging legal marijuana economy, which they said represented unprecedented wealth-building opportunities for people of color.

“He acknowledged that he hadn’t thought about ways to ensure black people had access to the legalized marijuana economy,” Campaign Zero’s policy analyst and data scientist Samuel...