Look, the idea is fine... but nullificiation has been discredited and rejected since 1809. U.S v Peters Why would we as a country want to deal with it again?
so just to be clear, you oppose WA and CO's laws too?
Not Quite... At this point, given the popular opinion in favor of legalization, it makes more sense to have restricted recreational marijuana than banning it outright.
Also I'm uncertain whether marijuana legalization is/should be a Federal or a State issue.
Well by your earlier reasoning it doesn't matter. Federally it is illegal thus CO and WA are wrong to nullify federal law. You cannot criticize the entire notion of nullification but leave random exemptions.
Also, since when is public opinion for allowing industrial hemp not at least the same or greater than recreational? Following your (sound) logic which pointed you to believe WA and CO are not in the wrong, the logical conclusion for states legalizing hemp should be the same.