The terminal aspect of the illness played a big part in helping him self justify at first on top of the pressures of the financial situation. A lot of very terrible bad things can be justified when you think you are going to die anyways, and WW's personal belief that life had both owed him more then he got and then punished him with cancer anyways let him sort of pretend he was just doing evil to earn a punishment he had already been given. I think a financial problem on it's own wouldn't gave done it.