Politicians love sitting in committees to devise such things as written constitutions. The fallacy is to believe that they guarantee something. Stalin no doubt operated under a written constitution guaranteeing all sorts of democratic rights. Hitler came into power under a written constitution with complete legitimacy. Modern Germany is a democracy not because of her constitution, but because of the determination of her people that it shall be so.
Mr Barnett wants a clean slate, but there is no such thing, as recent history, from the USSR to Ireland, via Yugoslavia, demonstrates. Gavin Lyall once made the observation that freedom and democracy don't depend on constitutions but on the ability of the people to say, "Hey, you can't do that!" Or, if you like, on eternal vigilance. A guarantee created by politicians is a paper shield.