Many people expect LKY to be rational and intelligent when faced with reasonable question. As such, we do not prepare ourselves for a polemic exchange. It was not the fault of the PhD student who probably just wanted to hear that logical answer. But history tells us we are not safe whenever LKY is in the room. We must always be prepared to face down an ideological diatribe from LKY. We must rehearse mentally what we are to do - we cannot wait till we are in the heat of battle to start thinking from scratch.
Here's what I've done in the past, albeit to a lesser light. I asked a question and got a response in the form of a question designed to diminish my credibility. I was quite intimidated but managed to compose myself. When he stopped talking, I ignored his question and repeated mine. I got a rant about something or the other, but mainly suggestions that I should not be asking the question. I waited until there was a pause, and repeated my question. Same rubbish from him. When I could, I said, 'it's obvious you do not have an answer to my simple question.'
I then returned to my seat. He was quite stunned.
As I've said, this is not easy under the pressure of public speaking, it has to be rehearsed.