I agree with Tom Knapp: the Barr-Root ticket deserves a clean slate, but not a blank check.
I tend to agree with Barr critics who will be watching him for backsliding on DOMA and drug prohibition. Neither of these is one of the LP's Big Three Franchise Schisms on whether the U.S. should enfranchise those who are unborn (e.g. not to be gratuitously killed during eviction) or who are outside our borders (e.g. to always be allowed to migrate here, or to never be defended by us from tyranny there). The LP should be ecumenical toward a libertarian like Ron Paul who deviates on the first two schisms, or toward a libertarian like Starchild who deviates on the third.
But substance use and marriage are about the individual rights of adults for whom none of us questions their equal franchise under U.S. law. Federalism is an indispensable strategy for 1) dividing and conquering the nanny state (e.g. through Tiebout sorting) and 2) letting states compete to outrace the federal judiciary in recognizing individual rights. However, federalism is not an end in itself, and we are not the Constitution Party.
If Barr's position on drug policy is just that it should be defederalized, then I guess I can live with that if Steve Kubby can -- as long as Barr doesn't speak in favor of states conducting their own wars on drugs, or in favor of the feds taking the drug war overseas.
DOMA, by contrast, seems specifically designed to undermine competition among the states in recognizing marriage equality. We wouldn't support states being able to deny full faith and credit to mixed-race marriages, and we shouldn't support states being able to deny full faith and credit to same-sex marriages. Our new Platform is very clear: "Sexual orientation, preference, gender, or gender identity should have no discriminatory impact on the rights of individuals by government, such as in current marriage, child custody, adoption, immigration, or military service laws."
We are the Libertarian Party, not the Federalist Party. We should treat the U.S. Constitution as a sword with which to divide and conquer the nanny state. We should not let the Constitution be a shield that protects 50 nanny states from condemnation by the LPUS. "We, the members of the Libertarian Party, defend the rights of the individual" -- and that defense must not be constrained by how the U.S. government currently happens to divide up responsibility for invading those rights.