The Nature of Sin : Chet HaEigel

[muman613]

In this Shabbats portion we read the story about the Sin of the Golden Calf.

Many commentators explain what the nature of the sin was. Was it purely Idolatry? Was it something a little less severe than Idolatry? Why would the Jews who had just heard the word of Hashem at Har Sinai fall so low within a few weeks? Were the Erev Rav so convincing that the rest of the Jews came along and joined them in building a Golden Calf?

Why did Aaron build it? Shouldn't he have tried to persuade them to wait for Moses?

Of course we know that HaSoton was trying to make the Jews give up on Moses because he was late in coming down from the mountain.... But I am interested if anyone else learned reasons for the Chet HaEigel...