Agreed, trisher. If you look back in history, there are so many times when you ask yourself how things reached such a point. With hindsight, it's possible to pinpoint past decisions, which contributed to later events. Nazi Germany is the obvious one, but there have been others. That's what makes history so fascinating. It's always a question of 'what if...?'
I'm not accusing Theresa May of being a megalomaniac (I hope), but we just don't know who will be PM in 20 or 30 years. Only 25% of those eligible to vote voted for the current government. Theresa May became PM by default. It's difficult to argue that she has a mandate from the people to act alone, which makes a mockery of democracy.
What would happen if in the future we have a PM who really is a megalomaniac? He or she could act alone and overrule parliament on just about everything. He or she would even be able to change laws without consulting parliament and could use notification of Article 50 as a precedent.
If this future megalomaniac has the media and police/armed forces under control, he or she could appeal directly to the 'people' by offering some kind of sweetener, which might even justify abolishing parliament. If you look at the history of dictatorships, there is often that kind of background.
It really is that serious. It's about the relationship between parliament (of all parties) and the cabinet, as well as the relationship between MPs and constituents. Without a US type constitution, this kind of constitutional crisis has been part of the history of the system we now have.