Indeed Mr McDonnell gives with one hand and takes with the other. He gave when he said he was impressed Benn's speech. And he took when he finished off by stating the following:
“I’m always anxious that the greatest oratory is going to lead us to the greatest mistakes.”
Mr McDonnell is right - great oratory can be a disguise for great falsehood. Think of Hitler - the Master Orator.
However, there was nothing to stop a skilled oratory putting the case against air-strikes or war generally. Think of Neville Chamberlain's “peace in our time” speech. That only became renowned after-the-fact. Indeed even though Chamberlain was shown by history to have been a naïve and gullible appeaser, his speech can still be seen as fine oratory. So, yes, Mr McDonnell, “the greatest oratory” can “lead us to great mistakes”. Indeed great oratory can take people in all sorts of direction.