When the Russians surrendered in 1917, the Germans forced them to sign a very harsh peace treaty (the Treaty of Brest Litovsk). The Russians had to give Germany lots of money and some of their land. Surely this means that the Allies are justified in being just as harsh to Germany at Versailles.
The treaty of Versailles was far to harsh on Germany, The massive economic disaster was a driving force for the Nazi uprising. The treaties main holdbacks for Germany were eventually ended by Hitler and the Nazi party would have had far less support if the other European countries hadn't caused their economic collapse.