According to the Midrash (Shemot Rabbah 21:7, Zohar 2:170b), an angel was accusing Israel and claiming why Hashem should save them and drown the Egyptians: "Just like Egyptians, the Hebrews are also worshipping idols, so what's the difference between them?"
(Somewhat later, the version in Zohar mentions more specifically that is was hard for Hashem to get through the strong Attribute of Judgement.)
What kind of claim is this? Obviously there is a lot of distinction between the two groups. It sounds like confusing the victim and the perpetrator!
What is so bad about it that some Jews indeed assimilated and worshipped idols, in a time that they were not really commanded not to do so (besides the prophecy of Aharon)?
Obviously the Jewish camp was full of good middos, incredible potential, inherited from their forefathers, and they were just about to approach Har Sinai to to receive the Torah. Given the fact that there were ample answers possible, what exactly this Attribute of Judgement wanted to achieve with such a seemingly simplistic question?