And what will you give me in return, Severus?' 'In - in return?' Snape gaped at Dumbledore, and Harry expected him to protest, but after a long moment he said, 'Anything.
I'll tell you what's the greatest power under heaven, and that is public opinion-the ruling belief in society about what is right and what is wrong, what is honourable and what is shameful. That's the steam that is to work the engines.