'Vaccines cause autism' gives people a weird sense of comfort. You can direct all your anger and frustration at them, Big Pharma or doctors or whoever sell vaccines. They purposely cause autism, just for money. Because, what's the alternative? The truth? 'We don't know what causes autism, but it's definitely not vaccines. No, we can't tell you what does cause it and we can't cure it. It'll just randomly happen to some people without any reason and there's absolutely nothing you can do about it.' People would rather live in a world with a clearly defined monster they can fight than a nebulous lack of information.