The idea that the Treaty of Versailles was too harsh on Germany is a myth. I'm more inclined to blame the outbreak of World War II on other factors, such as:

1. The Great Depression, basically unrelated to World War I/the Treaty of Versailles, devastated the world economy and, when economic times are tough, people turn to radical political leadership, like the Nazis (there was even clamoring for dictatorship in the United States during this time period...see the 1933 film Gabriel Over the White House, which depicts the President of the United States being possessed by an angel and becoming a "benevolent" dictator to deal with the Depression and rampant gangsterism).
2. The stab-in-the-back myth (also known as the "Big Lie"), which stated that the German military had not been defeated during World War I, only betrayed into surrendering by the Jews, Freemasons, and social democrats, was pervasive in German culture after World War I. Even social democratic German President Friedrich Ebert contributed to the odious lie by welcoming returning troops with "No enemy has vanquished you." The stab-in-the-back myth was especially promoted by Erich Ludendorff (former co-commander of the German military with Paul von Hindenburg and former co-military dictator of Germany with Hindenburg) and Adolf Hitler, who both led the Beer Hall Putsch in 1923.
3. The United States' rejection of Wilsonianism after World War I meant that the United States would retreat back to the Western Hemisphere and ignore European and Middle Eastern affairs. The U.S. refused to join the League of Nations (and refuse to establish a protectorate over the new country of Armenia, meaning that that new state would be wiped off the map by Turkey) and, with Great Britain tending to its own empire, left France as the only leader of the world. The United States would learn the value of Wilsonianism with the Second World War and become a founding member of the United Nations and NATO.
4. The Treaty of Lausanne with Turkey following the "Turkish War of Independence" essentially legalized genocide. Turkey would get off the hook for its horrific genocides against the Armenians, Assyrians, and Ottoman Greeks during World War I, inspiring Adolf Hitler. Only proper punishment against Turkey could've prevented this unfortunate outcome of the "Turkish War of Independence."
5. The new democratic German government, the Weimar Republic, had somewhat weak democratic institutions and was fraught with political violence between the left and the right.

One reason for the "Treat of Versailles was too harsh" myth has to do with the "there were no bad guys in World War I" myth. In reality, the Central Powers were committing atrocities at almost every turn. Germany had its reprehensible Rape of Belgium and its use of Belgians Poles as slave labor. The Austro-Hungarian Empire and Bulgaria committed genocide against the Serbs. The Ottoman Empire's nightmarish genocides against the Armenians, Assyrians, and Ottoman Greeks have already been touched on. The Allies of World War I had no such record of mass crimes against humanity. Well, Czarist Russia committed some cruel atrocities, but, by mid-1917 (with the democratic February Revolution in Russia, not to be confused with the communist October Revolution in that country), the Allies of World War I were arguably more democratic than the Allies of World War II (who had to rely on vicious dictatorships like the Soviet Union and China to do a lot of the heavy lifting).