But managers rely on engineers to let them know when some compromise can be made and when it is absolutely vital not to do it.

But management also relies on customers to tell them which compromise is vital to selling a product. And in a market with such huge price-pressure as aeronautics, I can easily see how this is going to override engineer's concerns.

I don't think that any Boeing customer have said or implied that it's OK if a plane can crash as long as they save up on pilot training.

Of course they didn't; the damage to the airline's reputation would be terrible. The customers didn't make this choice; they were deceived by Boeing, who sold them on the idea that they didn't need any significant new training for this disaster of an aircraft. The customers didn't design this thing, they just bought it after listening to Boeing's promises.

Didn't they "vote with their wallets"?

They certainly voted with their wallets for a plane that doesn't require additional training. But they sure as hell did not vote with their wallets for a plane that does that on expense of crashing. And, to reiterate my point, I think that managers who pushed for trade-offs between different objectives did not push for this particular trade-off either.

Well, that's the law of unintended consequences. Customers wanted so not pay for retraining, Boeing wanted to get to the market faster and not wait for re-certification, managers wanted a physical problem fixed in software - and in the end the envelope got pushed too far.

I am sure the company operating the Titanic didn't exactly strive to have a shipwreck either.

This is true, but it is a statement about causality and the thread was about responsibility. Those are two different things. The fact that your actions lead to a certain outcome does not automatically mean that you're morally responsible for this outcome (that's the fallacy that leads to victim blaming, among other things).

It is always engineer's responsibility to clearly explain the trade-offs to the managers. Only a manager who's making the decision with accurate information can be responsible for it.