It is extremely easy for one bad person with a lot of money to put bad ideas into the heads of hundreds of millions of people, causing them to believe they arrived at the idea themselves.

The only defense against this form of manipulation is critical thinking.

Very few people are capable of it.

Of those who are capable, very few bother to do it, even when it matters.

Only those people who can and do think critically when it matters can be trusted to have ideas that are their own. Everyone else is just doing what they're told, and they don't even know it.