[lmkg]

This is sorta-kinda true, but not quite. While the residents of a state are technically held to the union of state and federal laws, the jurisdictional issues are important. If a state declares something legal, that means that state-level LEOs won't enforce the federal laws. Those laws are still in effect, but if you're a deadbeat twenty-something toking up behind the liquor store, you care about the subset of laws being enforced by the local beat cop, not those being enforced by the FBI.