Maybe he's realized the inevitability of the situation and decided to jump ship. Can't completely blame him, but makes it difficult to take his opinions seriously.
A better way to react would be 'it looks like he's done bad things, so when he talks about those bad things, he knows what he's talking about and we should take his opinion very seriously. Whether he should be punished is a separate question, but if so, that punishment should take a form that doesn't cripple our ability to stop the other people who are continuing to do those bad things.'
I don't think anyone is arguing with 1.