I can remember Corbyn being grilled on 'would you press the button'. He stood firm when it would be all too easy to say 'yes, if the circumstances were so bad, I'd press it'.
But he didn't do that. He argued (correctly) in my opinion that it would be futile anyway. 10 million dead as opposed to 5 million? escalating a nuclear war further? bonkers.
He's not completely stupid - he knew it was hurting him politically, but he stood firm.
He did the same when being accused of being an IRA sympathiser. He argued that at some point, you have to talk with those you oppose. The British government was doing all sorts of behind the scenes stuff with regard to the IRA, but he expresses his honest and open view and he's the devil incarnate.
I don't think he's good for the Labour party, but that's because politics is far less about policies and more about personalities. In media terms, he's not too appealing. Boris Johnson is. But Boris Johnson will turn policy and principle on a sixpence to win votes.
I don't have to agree with everything he believes, but I can see a principled man.