Carter has been ballsy as a former president. Most of these guys just rake in money from speaking fees and corporate 'consulting', but Carter has stuck his neck out and written extensively about apartheid Israel, its fifth column lobby in the US, and the detrimental effect our subservience to the Lobby has had on our national interests, national security, and fiscal solvency.
Every president since would like to speak up, but dont have the balls or the patriotism.