The main reason someone would say this is because Socrates could very easily have escaped his execution. You could say he is arrogant because he wants to stay and defend himself. He thinks that what he has to say is so important that he should defend himself rather than escaping with his life.
The main rebuttal here is that, by escaping, Socrates would have been betraying his own beliefs. He would have been allowing himself to be coerced into going against what he believed. For someone whose whole life was centered around a search for knowledge and truth, this would have been intolerable. Death was preferable to betraying his convictions.