The recent episode got me asking this question. To start off, his malicious ways seem to stem from eons of abuse from Megatron. He was always to some extent always trying to impress/amount to Megatron, particularly in Season 3 of Prime. His master, whom he is expected to look up to, always treated him like trash, and so he now holds great resentment to the point of wanting to kill Megatron. But beneath all that, I feel like Starscream is repressing the goodness and nobleness- so much so that he is completely oblivious to it. Think about it; When he served others, he accomplished a lot more than when he was on his own-- yes he would always failed nonetheless, but he got closer to victory when being more noble (as noble as he could have been, at least) than full-on treacherous. Its as if Starscream was born to be noble and good, but was lead astray down a dark path that corrupted him, and imprisoned his goodness in a place where Starscream would unlikely ever free his goodness. This is furthermore supported by the fact that the Dark Star Saber (which, may I remind you, is made from the blood and essence of the Transformers' god of evil himself) rejects him. Starscream was a bot made for goodness and nobility, but fell down a path of malice and corruption. He was meant to serve others in the name of goodness, which explains why he fails at everything malicious, but goes a little further when he is serving Megatron (because it subconciously comes from a place of nobleness). He resents Megatron for abusing him when all Starscream ever really wanted was to impress and serve his master. The Dark Star Saber rejects him because of that goodness that remains hidden deep within his spark. I am not the best speaker, so I apologize if this didnt make too much sense, but I hope you guys can understand what I am trying to suggest.