Totalitarians start at the bottom - disarming citizens, stopping free speech, taking control of heath care and services people are dependent upon, targeting 'enemies of the State' with IRS etc... - and work their way up...
Ben Carson's talking about 'the birthing' of a totalitarian State... he's NOT saying Obama is putting humans in ovens or rounding them up for camps. Carson's saying the stage is being set...in it's typical fashion.
In all fairness, the French Revolution and Reign of Terror didn’t even bother with the disarming of citizens. If anything, they supplied citizens with guns specifically so they can gear up a mass killing from the start. And I know there were reports of people actually laughing and cheering when a guy was shot with shotguns. You can read all about it here: http://www.culturewars.com/CultureWars/Archives/Fidelity_archives/parricide.html
And bear in mind, the French Revolution is what ultimately set up the likes of Communism and even Naziism.
But beyond that, yes, Ben Carson is indeed correct, at least regarding the Nazi Germany comparison.