I think that history can be a good counselor, if you use it right. Ever heard the saying "History repeats itself?" If Ar-Pharazon had paid attention to other's mistakes - pride, need to control - maybe he would not have made the same mistakes seeing the disastrous results. And surely he had heard stories about the Noldor, how Melkor had lied to them? It is actually very similar, and hearing the name Melkor come from Sauron's mouth should have put up red warning flags in his mind.
It was, I suppose, rather stupid of him not to pay any attention to history and listen to Sauron. I'm not saying he's stupid (Though he really isn't very smart either), just blinded by his desire for immortality and control. And Sauron's lies were subtle, and like Melkor before him, he probably wove lies and truth together so that Ar-Pharazon couldn't tell the difference.
Does it sound like I like him? I'm certainly trying to defend him well enough. I don't. In fact, he is one of my least favorite characters. Marrying his cousin and taking the throne wrongfully is pretty bad. Maybe I'm just enjoying playing devil's advocate.
