Obamacare is only one example of a bad law that would've never passed had it not been for the 17th Amendment. 26 states sued to have O-"care" struck down. Assuming those states' legislatures would've instructed their DC delegates to NOT vote for it, 26 states = 52 senators = the law would've never passed. Just one example.
Use the 5th to strike down the 17th, and amend the 14th.
Scouts Out! Cavalry Ho!