But the reason for that is not the supposed "benevolence" of "superiority" of the Anglo-Saxon regimes - the inventiors of modern day slavery, the genocide, and the concentration camp (the last two titles go to the British for their performance in Tasmania and South Africa, as well as to the US-ers for their treatment of Native Americans). The difference between Nazi Germany on one side, and the Anglo-Saxon genocide machine is mainly in the skin color of their victims, and the winning of the war. As a result, nazi historu has been written, for the most part, by its white skin victims. Had the history of the British and US empire been written by its dark skin victims, "democratic institutions" you mention in this context would have a similar meaning to "Demokratische" in the context of "Deutsche Republik."
When sufficiently threatened, the Britsh and US regimes were as brutal as the Nazis, as they have ample opportunity to demonstrate. However, the historical span of these regimes is much longer, spread over a much larger terrotory, and involving very different time periods than the Nazi Germany.. Therefore, any comparison of these two regime types is really comparing apples and oranges. Comparing Nazi undemocratic practices from the WWII to more democratic practices in the US at different times in history makeas as much sense selectively comparing episodes from the US history, such as the Native American genocide, slavery, or lynchings, by "pairing" them with similar episodes from the nazi history, like the Kristallnacht, labor and death camps.
The bottom line is that there is nothing that would "predestine" Germans but not US-ers to develop a fascist regime at some point in history, and vice versa, nothing that would prevent either from so doing. As you correctly observed, comparing factual events to counterfactual ones are speculations that cannot be proved or disproved. Havingsaid that, I think that the US is now pretty close to nationalistic authoritarianism - and it is beside thepoint whether we call it fascism, or say that US managed to avoid it before. So did Germany before 1933. There is always the first time.
PS. How you got to the Holocaust denial from here is beyond me.
Wojtek