I think it's very difficult to be in the performing arts and not become indoctrinated into a form of groupthink, both here and the US. It's pretty much a sealed little bubble and because of the incestuous nature of that world where a hint of wrong think will put an end to opportunities, people just conform.
Added to that, these are people who spend all day creating fantasy and playing make believe so notions of 'authentic self' and 'you are who you say you are' probably resonate deep into the actor psyche to the point it probably feels personal on some level.
It will also be viewed, subconsciously or otherwise, as a status thing. These are the elite status beliefs to hold so if you aspire to be part of that group then you must believe these things too because how else can you manifest destiny and make it in such a competitive, crowded industry?
It's fascinating really but bears very little reality to...reality and the lives of people not in an industry bubble.