Brainwashing

Sometimes I think the term "brainwashing" is a subjective judgment of highly effective persuasion. Simply put, if someone's personality and opinions have been changed in what is deemed to be a positive manner, that someone has been persuaded. If the change is in a perceived negative direction, that person has been brainwashed.

That bewilders me, because I am trying to better understand just what brainwashing is, and how to differentiate it from plain persuasion. The loose way the term is bandied about does make me think that the terms brainwashing and persuasion are interchangeable depending on the arbitrary perspectives of the people deciding the label. For example, if someone suddenly decided to join an unpopular cult and started becoming exceedingly devoted to the cult, brainwashing is suspected because the person was not expected to originally be of the temperament that would nudge them towards cult membership. And given that the cult may be deemed detrimental to them, their devotion to it may be seen as yet another sign of brainwashing.

However, I've always wondered if they were indeed "brainwashed" as the term is understood. It may well be that the person genuinely believes in this cult for whatever reason. In fact, the term "genuinely" is dubious as well, since it may well be that the brainwashed individual and the persuaded individual both truly believe that they are devoted to the cult. How will one distinguish at this point? My current take is that perhaps the terms are differentiated by perceived acceptability of the persuasion, rather than any objective measure of brainwashingness. After all, I haven't heard of people being brainwashed into being perfectly good law abiding citizens. They were...persuaded.