From a strictly logical standpoint, they should either have been punished so harshly that they could never have inflicted damage again (like what the Spartans did a lot) or in accordance with Woodrow Wilson's 14 points plan, which is what America and Britain wanted to do anyway (it was France being in a sulk that pushed the Treaty of Versailles to be so harsh). Cause basically, what they did, was to make it harsh enough that everybody in Germany was pissed off and looking for revenge and international pride, but not harsh enough that they couldn't build up an army again.
But like I say, thats strictly logic. If you want a moral answer, you kinda have to decide for yourself.