Why did Great Britain and France ignore Hitler's foreign policies?

We, of course, have the luxury of high-sight and the simple answer is no. But back in the day it wasn't so easy to tell. The sensible thing for Hitler to have done was to be satisfied with his gains and not keep over-reaching himself. The Allies were hoping Hitler would be sensible and were surprised when he wasn't. Hitler you have to understand kept on over-reaching himself even through-out the thick of the war. (He should have never attacked Russia, or declared war on the US).

Now the allies had good reason to not get involved in a war with Germany as the German war machine was good. Look what happened to France. England would have fallen too if Hitler had kept his focus and not gone tearing after the largest military power in the world. (Russia)

Now consider the US's war on Iraq. Should they have left Saddam alone or was it better that they end up where they are now?