Odds are you’ve never heard of the “mudsill theory of labor,” but you and everybody else in this country really should learn about it. It explains a whole spectrum of Republican behavior that otherwise seems baffling and self-defeating. For example: — The past 7 years have seen a near-fivefold increase in documented child labor violations by employers. States have responded to this alarming trend in two ways: Democratic-controlled states are putting more teeth into their laws and upping enforcement; Republican-controlled states are loosening their laws and cutting back on enforcement so childr…