> This is exactly how online political campaigning works these days.

Not just online propaganda. All propaganda.

> That's why billions of Facebook ads spreading 'fear and uncertainty' over things like immigration and borders etc.

It isn't "billions" of facebook ads. It's human nature. Fear of the other is why we have borders in the first place. Do you have a home? Lock the doors? Etc?

> did so well to get so many people to vote for things that were against their interests, without them realising it. Like Brexit.

Ever consider what ads provoked your reaction?