He tries to fool his audience in unbelievable ways.

I applaud Derren not because of his shows but because of his effort to show something as "true exposure" when in reality he clearly doesn't see it so. For example, on the "Dead people" guy he clearly didn't believe in psychic ability. That's true so far. What isn't true is that Derren very well knows there's not only Cold Reading. He portrayed though the whole fakeness to be attributed to cold reading. This was unbelievably deceitful. He has explicitly used other methods in the past such as Hypnosis that can inflict much more impressive results than cold reading. However, he completely fooled the audience as something that is clearly only cold reading. He does it because he doesn't want to say the whole true because a) he gives away his tricks but also b) some people won't even believe him.