It is comparable to Nazism and Fascism in terms of it's methods of dictatorial rule, but has very different system of ideology and motivations. There is considerable debate on this point as to which is more important, reflecting deeper issues over the conflict between means and ends.
One thing that I've observed is that, at its most basic level, Nazism/Fascism, Communism/Socialism, and US-style Liberal Democracy all have one thing in common: They all claim to reflect the will of the People. Nazism emphasized the German "Volk" as being their central focus, and the Fuhrer was seen as the physical embodiment carrying out the will of the people ("I am Germany"). Communist regimes also focus on "The People" as their top priority, as in "People's Deputy" or "Enemy of the People." And in our own U.S. Constitution, we have as the three most prominent words at the top: "We The People."
So, all of these systems advocate the basic principle of "Power to the People." All of these systems are nominally "democratic" and "constitutional." It's just that in Nazi Germany, Hitler's dictatorial powers were supposedly only a "temporary" measure during a manufactured "crisis." Once the Army gave their loyalty and took an oath to Hitler personally, then that was that. As with Mussolini's supporters, the conservative aristocrats may have seen Fascism as the lesser of two evils and considered that right-wing extremism could be justified as a necessary response to the left-wing extremism they were facing from the Soviet Union and their perceived left-wing allies in other countries. No doubt there were many who believed (rightly or wrongly) that their country was in mortal danger and that they were surrounded by enemies.
The Soviets were also viewed as extreme, although they also felt vulnerable and surrounded by enemies - as Russia has been invaded countless times throughout history. Moreover, the trauma they suffered during WW1 and the Russian Civil War was still fresh in the public's memories during the 20s and 30s. Stalin was able to gain power using more of a "divide and conquer" technique. He was appointed to General Secretary only because Trotsky and Zinoviev turned it down. Neither one of them thought very highly of Stalin. They thought that he wasn't very bright - just a useful bank robber and gangster to serve the party's interests. Trotsky called him "the great mediocrity of the Party." But they underestimated Stalin. Whatever checks and balances were in place to prevent one person from gaining absolute power failed largely because those who could have stopped him wasted their opportunities to do so. Stalin also gained a great deal of support from those who also believed they were fighting an "extreme" enemy, and therefore, extremism is the only way to fight them.
As to the OP, my point was to say that if a population is traumatized enough and scared enough, they could likely be persuaded to more readily support a dictatorship over a more democratic-republican system we generally favor in the West. But we never faced the same level of threat to our national survival as other nations have faced. We haven't seen a war on American soil since the Civil War - although that by itself could be seen as another type of "necessary extremism." Our government has also generally avoided giving absolute power to a single individual, although even that can be seen as a bit iffy. But overall, we've taken the route of implementing various liberal and progressive reforms on a somewhat slow and incremental basis. This has had the effect of finding a middle ground between opposing factions and kept things relatively peaceful, as long as reasonable voices prevail and there is an overall willingness to negotiate and compromise for mutual benefit. This was not the case in pre-revolutionary Russia or China, as both sides were so firmly entrenched and has such a long-term enmity towards each other that no "non-extreme" solution would have been possible.
Now, I fear that's where we might be headed in America, since there has been long-term ideological entrenchment which seems to be getting worse. This is what could lead to greater extremism, since there appears to be fewer bases for any compromise. During WW2 and the Cold War, different factions might have been able to compromise for the sake of national unity or the greater good, but a lot of those motives seem to have fallen by the wayside in more recent years. US patriotism and nationalism seem to be less and less relevant in a global economy with more widespread and advanced means of communication and cultural exchange. And yet, there are still many who argue that US militarism and interventionism are "necessary evils" because "we're surrounded by enemies" (more or less). That's generally the same refrain which is repeated over and over.
During the 60s, things seemed like they would go in an extreme direction, although the left got distracted by sex, drugs, and rock & roll. Once the right fed them their sacrificial lamb (Nixon), the left then mostly sold out to consumerism, while maintaining a veneer of social liberalism and hippie nostalgia that still made them "cool" in their own self-serving, narcissistic way. But those days are over, and the gravy train has been sputtering as of late. I think that we are getting to a point where extremism from either the left or the right is conceivable, possibly even foreseeable if factional entrenchment continues over the long-term.