Firstly, for the opposition towards the Nazi Party and the assassinations attempts upon Hitler, personally I'm not entirely adept at this particular topic so hopefully somebody else could answer these more fully, however, I am aware there were in fact several opposition groups. One notable group is that of the White Rose who formed in 1942, so quite late into German Nazism's life cycle, and were comprised of German students that non-violently demonstrated against the Party. Yet for the major threats considered by Hitler, particularly any Communist movements, they were largely captured and driven into concentration or labor camps for 're-adjustment' so to speak.

However for the culpability aspect of your question I can be more astute. Crucially the Nazi Party itself was democratically voted in as the majority party within the Reichstag by the German people, so there was clear considerable support for Nazism even before Hitler established his full dictatorial rule in the 1930s. I highly recommend reading 'Modernism and Fascism' (or any of his other works) by Professor Roger Griffin, I've recently studied under him at university and he offers a seminal understanding of interwar Nazism and its appeal for the German people. Basically, the impact of the First World War must not be understated, the war for the Germans (and also the Russians) destroyed any confidence in the security and prominence of the old systems, particularly liberal democracy and traditional religious beliefs. This insecurity fed the development and succession of Nazism into German society, as Nazism, although often not perceived as such, contains a powerful ideology. Griffin hypothesises that at its core both Fascism and Nazism center around an ideology of 'palingenetic ultranationalism' which means a cultural rebirth. Advocated through a powerful, singular leader such as Hitler or Mussolini, this ideology worked to offer an alternative to liberal democracy and amalgamated the good qualities of German ancient history/people (Aryan qualities) with modern technology to ideologically produce a 'new' society that would rise above the degradation witnessed after the war. Subsequently, I believe the German people should not be blamed for allowing the rise nor were they captives of the regime, I think the sheer desperation of the 1920's and early 1930's drew the majority of German people, as it also did for the Italians, to the alternative ideology strongly advocated by Hitler and his Party.

Amongst German historians there is the term 'Sonderweg', which translates to 'Special Path'. This is the idea that German speaking countries had a unique path from pre-modern landed class societies to the modern industrialised state, which contributed to the rise of totalitarian fascism. Looking at the 'Sonderweg' debate amongst historians can tell you a lot about the extent to which the German people were responsible for the rise of National Socialism.

Historians such as Franz Fischer and those associated with the Bielefeld School have claimed that there were in fact special conditions in Germany that led to the rise of a certain militaristic class that was able to conduct an aggressive sabre-rattling foreign policy towards other countries in Europe. This class helped trigger The First World War, and whilst not as influential in the immediate aftermath of this defeat, they resurfaced after the economic collapse of 1929 to contribute to the downfall of the Wiemar state. Von Papen and Hindenberg are two recognisable names from this class, and it was these people who essentially handed Hitler power in the early 1930s. In addition to this militaristic strain within German upper crust society, there existed a specific form of irrational mysticism, that is seen in the works of anti-enlightenment thinkers such as Otto Weininger, J.G. Hamman and, later on, Martin Heidegger and Albert Schmitt. Fritz Stern has named this the 'Volkisch Movement', which is conventionally translated as 'populist movement', however 'folk [popular] movement' gives a better idea of what he meant by this term.

However, the 'Sonderweg' thesis has been criticised because many of the examples given to back up the idea of the 'special path' existed at some point in other European countries. For instance, France, Britain and Russia all had militarised aristocracies which gave way to a militarised bourgeoisie. In fact, France had a military dictator and harboured anti-enlightenment thinkers such as Rousseau and De Sade. It also had a strain of anti-semitism that is usually ascribed solely to Germany, which is demonstrated by The Dreyfuss Affair. The UK similarly had a number of number of prominent public figures who were able to publicly air antisemitic thought: Orwell in his essay 'Antisemitism in Britain' accuses H.G. Welles and many other prominent writers of expressing antisemitic sentiment in their writing. In fact, Orwell also claims that due to the Nazi persecutions, it became unacceptable to express such sentiment in public after WWII, but it still existed in private society. So the claim that Germany was the only nation to have sizable portions of its society who were receptive to fascist ideas is simply not true. The social critics Theodor Adorno and Max Horkheimer, who themselves narrowly escaped the Holocaust, claimed that the problems with the Nazi state were wider problems that afflicted a particular brand of Western enlightenment and the modern state. They escaped to the United States from Germany and were horrified by what they experienced there. They claimed that a similar brand of selfishness and narcissism that made a lot of people in Germany ignore, or actively capitalise on, the suffering of others was by no means a problem restricted to German speaking nations. Their claim can be summed up as that on the one hand, modern society held incredible technical and intellectual potential for the betterment of humankind, but at the same time as it was possible to mass educate and effectively produce medication to preserve life, it was now possible to mass produce death on an unprecedented scale.

In my opinion, and apologies if my answer has gone a bit off topic, but talking of National Socialism as a specifically German problem is unsustainable when you look at the history. Repressive measures such as eugenics, antisemitism and militaristic nationalism existed in most countries in Europe at that time, and even in the US. Perhaps as the loser of The First World War and with the reparations that it was burdened with by other nations, Germany was at this period able to have a receptive audience to this form of fascism in a way that allowed it to be successful. Aforementioned members of the upper echelons of German society attempted to contain these figures by giving them power, but they blundered, and gave them too much. However, attempts by an upper middle political class to contain popularism were seen in all the major countries across Europe during the inter-war years, especially after the 1929 Crash. In fact, it's worth remembering that Wiemar Germany, for all its contradictions, was unprecedented in terms of the liberal and progressive social policies that it undertook. However, (and this is the slight exception I take to the question), it is also worth remembering that fascism found a very welcoming audience amongst the upper classes in German (and British, and French) societies. In fact, it is arguable the extent to which the military attempts on Hitler's life were altruistic because they began to take place when it was becoming evident that Germany would lose the war: one of the earliest attempts on Hitler's life was in fact by a member of the working class: the carpenter Johann Georg Elser made an attempt on Hitler's life in 1939.