Asking cities to comply with laws on the books is so radical. 
Well yes, the Federal government forcing states to spend local money and resources enforcing a fiat from Washington IS radical. If we believe in any individual state sovereignty at all, allowing the Federal government to co-opt officials hired and directed by the states and forcing them to enforce some other authority's laws is the end of that sovereignty. I assume there would be more of an outcry if the Feds decided to order local police departments in Colorado to enforce Federal drug law, but the issue is exactly the same.
States' rights, the last refuge of someone who can't get their policies enacted on a national level.
