In many cases, I suspect that people adopt false beliefs and the ensuing dark-side for short term emotional gain, but in the long term the instrumental loss outweighs this.

That may be one way of adopting false beliefs the first set of false beliefs. Once the base has been laid (perhaps containing many flaws to hide the falseness), then in evaluating a new belief, it doesn't need to have short term emotional gain to be accepted, as long as it fits in with the current network of beliefs.

When I think of this, I think of missionaries, promising that having faith in God with help them through the bad times. Then after they accept that, move onto the usual discussion of Hell and if only you do what they say, you'll be fine.