Perhaps, but really you're just making Rhino's point. For a regime change to really work takes one with a rather large occupation for a long period of time. Our system of government wasn't built for that and the American people have no patience for it once it actually gets going.
Since we gets new leader every 4 to 8 years, no president wants to be bogged down in someone else's occupation, so they kill it. Same thing happened with Viet Nam. Should we have stayed there too? How is the Afganistan occupation going?