I think that Greek philosophy did have a very important impact on the time in which the philosophers lived as well as the present. The questions they introduced to thought are still present. In order to establish some kind of rules of behavior that will work, they had to approach the other questions first. To find some kind of purpose and meaning to our existance.
Mankind needs purpose for living and guidelines to live by.
I think history has been a pretty good example of what happens to civilations that do not have them.