I've always liked the weed issue as a jumping off point for getting people to think more seriously about state vs. federal authority.
Anyone who believes in "law and order" as the POTUS said he did has no moral obligation but to support the federal government in enforcing federal law. It's especially true for anyone who had a problem with Barry O. using executive orders to impact prosecutorial focus during his term. It's triply true for anyone who argues that the fed should crack down on sanctuary cities because those cities are acting in a way that contravenes federal immigration law.
People have to take foundational positions on this subject. Do you want the fed to brightline enforce federal policy and bring the states to heel? Or do you want the fed to relax its enforcement of these things and let the states chart their own course?
But the weird space where the fed strongly restricts state action sometimes and not others can't continue.