(1) Secession. This was used for evil in the form of slavery. But it is the most powerful check of federal power by the states we had. The fact it could be used for evil did not mean it is better to get rid of it.
(2) Expansion of the interstate commerce clause to mean basically anything. A main argument for why this can't be reversed is that it would destroy the civil rights acts, which acts upon even intrastate business. Rather what should have happened is 15th amendment should have been written to apply to private entities as well, instead of blasting away the interstate commerce clause.