What did Judas "betray," and why?
It may seem, for chronological reasons, that this topic should have preceded speculation about the "empty tomb." I saved it for last because for me, it's crucially important - the true climax of a discussion of the life, death, and significance of Jesus.
I don't want to offend any Christians who may someday be reading this. But as an agnostic and non-theist, I believe Jesus was nothing more than a normal, mortal man. I'd like to be able to respect him. But I can only respect him if I believe that:
(a) His disciples convinced him he was the Messiah, rather than the reverse.
(b) Under the circumstances, he saw the role of the Messiah as convincing more and more people that the Kingdom was at hand, and they should prepare for it by leading good, worthy lives.
(c) He didn't expect to be "rewarded" by being given an exalted position in the Kingdom.
(d) He didn't expect any of his disciples to be so crass as to want exalted positions.
Here's where the "betrayal" becomes important.
Dr. Ehrman doesn't believe it was necessary for Judas to aid the Romans by identifying Jesus. I disagree with him there. But it's a moot point, because I agree with him that the question we should be asking is why they were arresting him.
And why was Judas involved? Undoubtedly not for the small amount of money he might have been paid. It would have taken more than that to induce an actual disciple of Jesus to turn him over to a regime that would ultimately execute him.
Something must have turned Judas against Jesus. And given the sort of men they were, it probably wasn't anything as trivial as, say, rivalry over a woman.
It's possible that Judas had believed in the coming "Kingdom," but not in any kind of "Messiah." If so, the "Messiah" business would have irked him from the start. But he could have just walked away; there had to be more.
Remember all those crucifixes that show, over Jesus's head, the inscription "INRI"? The initials of Latin words meaning "Jesus of Nazareth, King of the Jews."
Dr. Ehrman has said that while the real placard over the cross didn't say exactly that, it's certain - due to multiple sources - that it did indicate that he was being executed for having called himself the (future) King of the Jews. The Romans probably didn't know that he expected their rule to be ended, not by him, but by heavenly forces. If they did know, it made no difference to them.
But there's nowhere in the New Testament where he calls himself that, or is called that by others.
As Dr. Ehrman sees it, he did - among his own disciples - call himself the future King. And that was what Judas told the Romans.
Of course, it's possible that Judas had turned against Jesus for some other reason, and was lying when he told the Romans Jesus had said something that would be punishable by death.
He might have had a different upbringing than Jesus, and been outraged when Jesus caused a disturbance in the Temple by railing at the moneychangers and overturning their tables. (Though according to Dr. Ehrman, it was probably a much smaller disturbance than the Gospels describe.)
And I've thought of other possibilities. Jesus was almost certainly born in Nazareth. Some people who expected a Messiah thought he'd be born in Bethlehem. Two Gospel authors would come up with implausible - and irreconcilable - stories to "explain" Jesus's supposedly having been born in Bethlehem. Might he himself have claimed he'd been born there? Might Judas have been appalled by the lie?
Or by another type of lie: Might Jesus have asked his disciples to spread the word - in Jerusalem - that he'd performed miracles in Galilee, when he really hadn't? I'm guessing there were so many fake "miracle workers" in those days, fooling the gullible, that a preacher couldn't expect to be taken seriously if he didn't make claims about miracles. And Jesus couldn't have faked "healings" and "casting out of demons," even if he'd wanted to, in rural communities where everyone knew everyone else. (The Gospel accounts of his miracles, written decades after his death, are the stuff of legend rather than fact.)
But there is a Gospel story (Matthew, ch. 19) that has to be considered here. In it, Jesus tells his disciples that "when the Son of Man shall sit on the throne of his glory," they will sit on twelve thrones, reigning over the twelve tribes of Israel! If we assume he's thinking of the Son of Man as a heavenly Being, reigning over the entire world, he doesn't mention himself. But Dr. Ehrman thinks it would have been understood that he would still be the disciples' superior, reigning over all Israel.
"King of the Jews."
(A later note: Dr. Ehrman is now saying he believes Jesus expected the Son of Man to make him ruler of the entire world. If any of this were believable, it would make a kind of sense, because he'd previously indicated that Israel would dominate the world.)
Not all the sayings the Gospels attribute to Jesus are authentic. Dr. Ehrman thinks this one is. He thinks a Gospel author would have been reluctant to include it, because Jesus doesn't seem to know Judas is destined to betray him. (That's the only problem he sees?) The fact that the author did include it shows that it must have been a very well-attested tradition.
I think this alone - with its assumption that the disciples wanted "thrones" - might have been enough to turn Judas against Jesus. He might have thought Jesus was "betraying" what their movement had initially stood for! Helping to save their fellow Jews - from death, yes, but also from oppressive human rulers. And not seeking "rewards" from God (as if eternal life shouldn't have been enough for anyone), but being humbly grateful for the trust the Almighty had shown in them.
Who was the saint, who the sinner?
Without more information - that we'll never have - I won't presume to judge.