Quote 1
"If it comes to that, which is the right side? How do we know that the fauns are in the right and the Queen (yes, I know we've been told she's a witch) is in the wrong? We don't really know anything about either." (6.60)
Edmund raises an interesting point here – he and his siblings are really just stumbling into the middle of a complicated political situation that they may not understand. Yet we as readers instinctively know that he is wrong. The Queen is obviously evil, and Mr. Tumnus is obviously good; that's how this book works!
Quote 2
"Because," he said to himself, "all these people who say nasty things about her are her enemies and probably half of it isn't true. She was jolly nice to me, anyway, much nicer than they are. I expect she is the rightful Queen really. Anyway, she'll be better than that awful Aslan!" At least, that was the excuse he made in his own mind for what he was doing. It wasn't a very good excuse, however, for deep down inside him he really knew that the White Witch was bad and cruel. (9.3)
Edmund may try to deceive himself, but, like Lucy and the others, he has an instinctive, fundamental knowledge of good and evil. The White Witch sets off all the alarms marked "evil" in his brain, but he tries to drown them out with foolish arguments and ridiculous reasoning.
Quote 3
"I say," began Edmund presently, "oughtn't we to be bearing a bit more to the left, that is, if we are aiming for the lamp-post." He had forgotten for the moment that he must pretend never to have been in the wood before. The moment the words were out of his mouth he realised that he had given himself away. Everyone stopped; everyone stared at him. Peter whistled.
"So you really were here," he said, "that time Lu said she'd met you in here – and you made out she was telling lies."
There was a dead silence. "Well, of all the poisonous little beasts – " said Peter and shrugged his shoulders and said no more. There seemed, indeed, no more to say and presently the four resumed their journey; but Edmund was saying to himself, "I'll pay you all out for this, you pack of stuck-up, self-satisfied prigs." (6.24-26)
Peter blames Edmund immediately and completely for the lies he told to make Lucy look bad. While Peter is sort of in the right, because it was wrong of Edmund to lie, his willingness to place blame on Edmund only increases Edmund's own sense of alienation.