If the human race were not hackable then society would not exist, we'd be the unchanging crocodiles of the last few hundred million years.

Have you ever found yourself speaking a meme? Had a catchy toon repeating in your head? Started spouting nation state level propaganda? Found yourself in crowd trying to burn a witch at the stake?

Hacking the flow of human thought isn't that hard, especially across populations. Hacking any one particular humans thoughts is harder unless you have a lot of information on them.