Explain Lucifer then. He and all the angels who joined him seem to be a case study in how angels are perfectly capable of doing evil and asserting their free will.
in islam lucifer was among the jinn ( invisible species lives on earth ) and they have free will, they are capable of doing good and bad
quran( سورة الكهف , Al-Kahf, Chapter #18, Verse #50)
And when We said to the angels: Make obeisance to Adam; they made obeisance but Iblis (did it not). He was of the jinn, so he transgressed the commandment of his Lord. What! would you then take him and his offspring for friends rather than Me, and they are your enemies? Evil is (this) change for the unjust.