I don't think this applies to the average MBA (full disclosure, I have an MBA). Most MBAs are just normal people who are just trying to do their job better.
Having said that, I guess some grads of the "most elite" business schools do that cultish thing you're talking about, but I would argue it has less to do with having an MBA than being a member of that top school. Those people tend to be the most visible representatives of MBAs while only being a very small portion of all people with MBAs.
Sure, they tend have high earnings, but this is the same pool that both want to and could get into a 'top' school which is a rather biased sample.
What you're saying seems akin to saying that a Stanford MBA is in less demand than the average programmer. (1) I think that's wrong. (2) It's really avoiding the point which his that being in demand doesn't really imply that those individuals will act more ethically.
Various euphemisms exist, like taking a break or the ever popular consulting. But, getting a job in school or being poached while employed is the happy path. Get off that path and it can be very hard to get back.
PS: I don't think demand changes the average much, but it's often outliers that stand up in the first place. So, I do think demand is meaningful as it reduces the burden of ethical behavior which impacts people at the edge.
An MBA largely has value because it acts like a cult promoting the networking between MBA's. It's arguably a great hack to extract value from organizations as opposed to customers.