Suffice to say I'm not entirely convinced by this argument.

The idea that Bismarck was somehow preferable to Hitler or that he deserves no blame for the latter is fantasy and hogwash.

Bismarck is infinitely preferable to Hitler, given that the former did not commit one of the largest genocides in history or start a world war. That he deserves blame for the rise of Hitler is a somewhat more complicated matter.

As you have mentioned, Steinberg's book was well received and praised for its readability and comprehensiveness. It brought together deep primary research and secondary reading. However, there is very little that is actually new in the book. There are no unseen primary documents consulted for the first time, no vastly different approach, just a retelling of the story which is one of the most retold in history. Similarly to Steinberg, the poster implies that Bismarck was an authoritarian who oppressed minorities and his political opponents and was anti-democratic. Nobody is denying this. However, block quotes do not an argument make. Where this post somewhat falls down is in the attempt to tie this to Hitler.

Back to Steinberg, where he does stray off the beaten track in his writing with the statement that Bismarck's legacy can be directly linked to Hitler (quoted in said post), he is criticised by his reviewers. Matthew Jeffries says of this assertion that:

these bold statements are perhaps the least convincing part of Steinberg’s weighty new biography of the Reichsgründer. Few who have studied the increasingly pluralistic and sophisticated political culture which developed in Germany in the decades after Bismarck’s fall will feel entirely comfortable with such assertions.

This particular argument is also not entirely new. Even while Hitler was in power, links were being made as far back as Martin Luther in an attempt to explain his rise to power. The general thesis of what is called the Sonderweg is that German history has been a history of misdevelopment. Where other European states developed along 'normal' lines and reached economic, social and political maturity roughly at the same time, Germany became an industrial state without having reached true political maturity. The result was that they naturally looked towards authoritarian rule and naturally when Hitler came along, embraced him with open arms. In the words of AJP Taylor, 'it was no more an accident for Germany to end up with Hitler than it is an accident when a river flows into the sea.' Our poster summarises their argument similarly: '[Bismarck] basically allowed Germans to think that they could modernize and become a great power without the liberalism and social upliftment that happened in America, England [Great Britain], and France.'

The Sonderweg argument in its purest form is, in my opinion, completely misleading and mildly racist. While certain elements are certainly true; it is unlikely that Hitler would have come in to power without the help of the Prussian elites, the core argument is based on a mischaracterisation of German society and history. Both of the other historians our poster quotes (Max Weber and Hans-Ulrich Wehler) are proponents of the Sonderweg theory.

Beginning with the Kaiserreich, both our poster and his historians seem to ignore the thriving political culture of the Second Reich. While Bismarck did his best to stop both the Catholics and Socialists, their respective political parties did very well. The socially conservative Centre Party often supported the post-Bismarck chancellors and by 1912, the SPD were the most popular political party in Germany, as well as the largest socialist party in the world. Election turnout in 1912 was 84.5%, a number rarely if ever reached in modern democracies. While censorship was widespread, political satire magazines such as Simplicissimus had a wide readership. The idea that Imperial Germany was an authoritarian dictatorship has largely been challenged in recent years.

Secondly, the Sonderweg thesis largely ignores the Weimar Republic, which was after all instituted following a popular revolt. Again, turnout in the 1919 election was 83% and pro-democracy parties gained the vast majority of seats and votes. The Weimar Republic survived several attempts by the right wing to overthrow it, not least by Hitler himself. While Hitler did eventually triumph, the 44% of the vote the Nazi party received at their highest point was by no means a ringing national endorsement from the German people, and the election itself was heavily weighted towards the Nazis.

There are other arguments against the Sonderweg, such as applying a global approach to the rise of Hitler, but those aren't particularly relevant to this post and are explored more fully in my sources below.

Finally, we come to the three similarities which apparently make Bismarck exactly the same as Hitler:

1. Both were ambitious outsiders who came to power by violating established norms at home and abroad.

One was a literal foreigner who only became a German citizen in 1932 so he could run in the presidential election. The other was a member of the ruling class with contacts in the highest of places. I'm also not sure what is meant by 'violating established norms abroad', as Hitler did very little of that during his rise to power.

2. Both had modest military experience. Bismarck far less so than Hitler who at least saw battle and so on.

Hitler had several years of combat experience and was decorated twice for bravery. Bismarck was a Lieutenant in the reserves.

3. Both on coming to power concentrated a great deal of personal power and acted in a very authoritarian manner, with little room for consensus, compromise and back-and-forth.

Hitler's style of leadership was actually fairly laissez-faire, I don't have enough time to deconstruct this fully, but Ian Kershaw's biography of Hitler goes into this in more detail.

Moving on to the reply, the idea that 'his success not only justified such actions in Germany, but also provided a model for Imperial Japan, Tsarist Russia, and modern Russia' is a whole different kettle of fish and one that, while I am sceptical, I lack the knowledge to deconstruct fully. The second paragraph of the reply brings little to the argument and I'm not sure what Henry Kissinger has to do with Bismarck.

In summary, the idea that Germany, aided by Bismarck, failed to develop democratically, resulting in Hitler, is incorrect. That Bismarck and Hitler were both violently nationalistic, good politicians and proponents of authoritarian rule is neither here nor there and does not support the argument made that Bismarck is somehow as bad as Hitler. The argument itself beyond the block quotes lacks a great amount of detail and as such it's quite difficult to analyse it properly.

Sources:

Jurgen Kocka, 'German History before Hitler: The Debate about the German Sonderweg'. Journal of Contemporary History, Vol. 23, No. 1 (Jan., 1988)

Helmut Walser Smith, 'When the Sonderweg Debate Left Us', German Studies Review, Vol. 31, No. 2 (May, 2008)

Jonathon Sperber, 'Review: Bismarck: A Life', The Journal of Modern History, Vol. 84, No. 3 (September 2012)

Robert Citino, 'Review: Bismarck: A Life', Central European History Vol. 45, No. 1 (March 2012)

Matthew Jeffries, 'Review: Bismarck: A Life', https://www.history.ac.uk/reviews/review/1123