If Krugman likes inflationary currency, he may use one. If you like deflationary currency, you choose yours. The problem arises when either you or Krugman starts proclaiming which one is "good for society". Then the guns are out and war begins.
I agree, but there seems to be hurdles. Anybody can possibly mint gold coins nominated in troy oz or gram, but if someone wants to create private gold backed paper money, I think the regulators may make hell for you. Maybe they will be taxed with sales tax. We need a law explicitely stating that private money is legal, that they are tax excempt, that anyone can freely change any kind of money for any other, and unhampered import and export of money.