DockJock, how far would you go into discretion to get home? How tired would you have to be to decide to stay put? How do you judge how exhausted a member of your crew is? How do you judge whether they are capable of doing their job? How competent would you be to handle a major aircraft malfunction after x hours on duty (insert the number you first thought of)?
The point here is that everybody is different. To have regulations, you have to put the power to choose to exercise discretion in the individual crew member's hands. Companies are, effectively, removing that decision, and telling crews they WILL come back into discretion.
I accept that you may well be compos mentis enough to continue, and most of us would probably prefer to get home. However, that is your decision, based on circumstances at the time. It is not the company's decision to make. That is where the danger lies.