We've all heard of brainwashing, but is it actually real? Can people be hypnotized or manipulated into acting against their own core values or best interests? The whole concept of brainwashing comes from the Korean War, when some American POWs made pro-communist statements or even refused to come home after the war was over. Of course, there were several reasonable explanations for this. Some of them could already have been communists- communism had a lot of American adherents at one point. Or the soldiers could have been tortured or starved or intimidated into making those statements. Or a few soldiers could honestly have been “converted” to communism through conversations with their guards.
That last explanation was the one that scared the government. At the height of the Cold War, the idea that anyone would actually choose to become a communist in preference to the American capitalist system was extremely threatening. So they come up with the explanation of “brainwashing,” a kind of hypnotic mind control achieved through sensory deprivation, humiliation and constant pressure.
Under the circumstances, the whole idea should be treated with some skepticism, but such techniques do exist, and may have been attempted by the North Koreans. The question is, are they effective? Most of the soldiers who experienced such techniques shook them off pretty quickly once they were freed and sent home. Cult groups try to use similar techniques, but most people who join a cult don't stay in it for all that long. This alone implies that the brainwashing can't be all that effective.
What I would suggest is that group-think is a dangerous reality, but that brainwashing in any other sense is not. In other words, if you choose to embrace the ideology of a particular group, you can then get caught up in a self-reinforcing network of conformity and uniformity of opinion that slowly leads you to abandon all your critical thinking skills and stop thinking for yourself at all, sometimes with tragic results. But no one can impose this on you against your will- if you don't make the initial decision to embrace the group ideology, no one can brainwash you into doing so.