It is science:
A study conducted by Daniel Bartels, Columbia Business School, Marketing, and David Pizarro, Cornell University, Psychology found that people who endorse actions consistent with an ethic of utilitarianism—the view that what is the morally right thing to do is whatever produces the best overall consequences—tend to possess psychopathic and Machiavellian personality traits…. Bartels and Pizarro found a strong link between utilitarian responses to these dilemmas (e.g., approving the killing of an innocent person to save the others) and personality styles that were psychopathic, Machiavellian or tended to view life as meaningless.
And there is your scientific connection between the man who advocates a happiness/suffering moral metric and the one who also advocates killing people for the mere possession of dangerous beliefs. They tend to be one and the same, and in the case of Mr. Harris, they are.