Justifications for Federal Regulation?

Rob:  What do principles of subsidiarity say about these arguments for higher-level regulation?

1.  Where activity in one state has spillover effects into another.   Does this show that local units can't handle the problem and therefore higher-level action is appropriate?  Air pollution blowing from one state to another is the obvious case.  But one might also posit that states that prohibit marijuana use will have their policy undercut by marijuana grown in California that seeps out of the CA medical-use market into other states.  (I suppose that might only justify a federal rule against transporting marijuana across state lines, but then the enforceability of that rule arises again as a question.)

2.  Where uniformity of government regulation, as compared with multiple state regulations, helps empower other subsidiary actors -- businesses, nonprofits, etc. -- by reducing the complications they face in understanding and complying with regulation.  (Assuming that there will be regulation, businesses -- at least interstate ones -- often prefer it to be federal for these reasons.)

Tom B.