Norfolk was a vile man by today's standards, but at the time was simply the head of a family, who actually came from almost nowhere, and had grown to be one of the most powerful families in the kingdom. He played the game - you had to. I'm not entirely sure whether he had a hand in Mary becoming Henry's mistress, especially seeing as she already had been mistress to the king of France. But I'm certain he was involved with both Anne and Katherine taking their positions.
I'm also not entirely convinced that Henry was the blood thirsty tyrant he is sometimes played out to be. The Tudor's had an incredibly flimsy claim to the throne as it was, and then the first born son died. Henry had seen first hand the panic and destruction caused by an unclean line of succession, and this was so driven into him that it was all he could consider. Which is one of the reasons I don't believe he was the father of Mary's children, as he would have acknowledged them in his desperation for an heir to the throne.