Two visitors were

It’s been a carnival down there under Tower Bridge. By the climax, you were lucky if you could push through the crowds in under 40 minutes.

That twisted viewpoint is so far removed from the message David is trying to convey, that I simply cannot understand how anyone could get it so badly wrong. And it baffles me that people will take the trouble to journey to Tower Bridge, push through the crowds, and then stand there complaining!
And then it occured to me that I had the perfect argument to silence the whingers. “Excuse me,” I said, “but I have suffered from a very serious eating disorder myself. I had bulimia, so badly that I could barely stand unaided at one stage. You don’t need to teach me anything about starving the body, because I know how hard it is to eat when every nerve and every muscle is fighting to reject food.”
The visitors looked disbelieving. You’ve never had bulimia, they said. But I was fired up now, and I told them the whole story – how I would rush to the bathroom after every course, gorging myself on platefuls of rich, creamy food and then voiding my stomach. The act of sheer willpower, I told them, was to force myself to keep food down – to overcome the compulsion to vomit, to accept that I was far too thin to be healthy. And that’s the core of the message that David is transmitting from his lonely box above the river: we are all in control. We dictate what our bodies need and do. We can master any compulsion, any craving. Every eating disorder can be beaten by the mind. When we wield the full force of our human willpower, nothing can stand in our way.