I am not Jewish, so holocaust trivializations just make me facepalm.
That's funny coming from you, as you make Nazi and Hitler references more often here than anyone else. I would even say it's one of your trademark go-to lines of argument, almost as much as your gratuitous sexual imagery.
Robinson's reference to Nazism is not as far-fetched as, for example, Cruz and Huckabee likening Obama to Hitler and his policies to Nazism. These days likening the President (or Bush before him) to Hitler is a crowd-pleasing way to show disdain and rabble-rouse. Back then WWII was still fresh in the lives and memories of all adults who voted in the 1964 election. No President before that year had been compared to Hitler, no President's policies had been compared to Nazi socialism. Robinson was reacting to the fear incited by the racism stirred up by Goldwater's arch-conservatism and viscerally was saying out loud what Jews and many other American adults feared in his saber-rattling militant attitude toward the Soviet Union. In the 1964 election the only states that Goldwater carried were Arizona (his home state) and 5 deep south states that had been targeted by the Civil Rights Act, and less than 40% of the popular vote nationally.
Like I said, because my family was Jewish we had the direct experience of Hitler and Nazism, and the creation of the state of Israel in our daily thoughts. Robinson had something to be afraid of, too, given his experiences as the first black Major League baseball player. I can't say whether he truly believed Goldwater could have become a Nazi-esque leader, but his "principled" stands for his own interpretation of the Constitution were deeply troubling to a great many people. Those principles, btw, are the genesis of hard-core conservative opposition to "liberal" policies today. Robinson did have plenty of reason to fear that Goldwater would speak for the goals of the most racist elements in society, as he had voted against the CRA and declared that the SC ruling in Brown v BoE was an abuse of power and should not be considered the law of the land.
But we (my family and most Jews) didn't think Goldwater would revitalize Nazism (though the KKK and other far right fringe groups declared their support for him) nearly as much as he would push the world over the nuclear brink against the soviets. In that way Robinson's own fears of Goldwater's extreme and unyielding views echoed those of many Americans.
FWIW, I didn't cite that article because of the single Nazi reference that you find so inappropriate, but rather because that year's convention was in its way a harbinger of today's mood among those Republicans who in their own way are fighting to defend racist and bigoted attitudes and are tossing around irresponsible militarist threatening language, all of which is worrying the mainstream majority of the American populace. It's unfortunate that both leading Republican candidates share that sort of following, though from different slivers of their Party's voters. If either one of them becomes the GOP nominee, which seems overwhelmingly likely now, I would hope they beat Goldwater's record for the lowest percentage of the popular vote received in any general election between two candidates.