It seems to me that the only really puzzling aspect to the rise of the Nazis is the Shoah. Looking at it today we see the Shoah as the defining characteristic of Nazism, but in 1933 Fascism was more about a vision for the future, and restoring order and prosperity
In the 1930s European democracy was young, capitalism appeared to have failed, the nation states were mostly fairly recent constructions, with disputed borders which didn’t really reflect ethnic and cultural boundaries, populations were growing at a speed never seen before, new technologies, instant communication, faster travel etc etc
Rapid industrialization had created a new and massive working class. The old order was clearly gone, and there was a deep divide between radical leftists and radical rightists about what the future order should be. Rural vs Industrial, religious vs lay, nationalist vs internationalist etc. Italy and Spain went Fascist, France was also highly unstable, with communists in a power sharing government from 1936 on, constant strikes and fascist rioting etc etc. The Spanish civil war supplied a stark illustration of where the polarization could lead, and the emergence of the Soviet Union was terrifying for the old order, the middle classes, the church…
So in the midst of this powder keg, the Nazis emerge, promising stability, prosperity, and even the empire that Germany had missed out on while all its neighbors were indulging only a generation earlier.
In the context, there’s nothing obviously unreasonable about twentieth century Fascism. Authoritarian rule, nationalism, military expansion, all apparently looked better than the ostensible alternatives, communism or chaos.
The real puzzle is how the iconically “rational” and “cultured” Germans could pursue a completely irrational policy of persecution and then annihilation against populations which ostensibly posed no threat.
A few weakish ideas :
The notion of human dignity is more of an axiomatic stance than a rational one, so if you don’t espouse the axiom…
Capital C Culture is often more sentimental than truly humanistic, rather than contributing to uplifting humanity it substitutes for it.
Is there anything specific about Germany that predisposed the Shoah - maybe… Germany was possibly more of an ethno-state than its neighbors, less of an ideological national story ? Less clearly geographically defined ? More fragile sense of national belonging, so more to prove ? Greater working class anomie due to greater industrialization ? Something religious maybe ? Italy, Spain and France were Catholic, and it was/is somewhat baked into their national identities.
TLDR, fascism is in no way incompatible with culture and reason, genocide is a way tougher knot to untie.