Foch was critical of the treaty since, among other issues, it left Germany as a united country. Considering WW2, one could figure that there wouldn't have been another World War with Germany as a major aggressor against the Western Allies if Germany had been thoroughly dismantled like it was after WW2. Or at least, that any Germanic movements hostile to the Western Powers would have a far more difficult time.
So, was there practical concerns that discouraged going further to dismantle Germany, or was it all down to faulty idealism?
The Allies had suffered pretty severe losses, despite having routed the German Army. Despite what /u/wunderbra said below (don't know why they did), the Allies would not 'ethnically cleanse' Germany; however, an occupation would have required thousands if not million of soldiers, and would have strained the Allied economies even worse than they already were. The Germans had stood down their Army, and had handed over substantial amounts of equipment; this was seen as good enough at the time. Moreover, Germany was needed as a buffer against the Bolsheviks, and even more so, was an important economic partner on the continent.