There is a growing fascist menace in this country, and with the Leave victory, they now have the upper hand. The rest of us have to realise that it's no longer business as usual. We are a minority. A large, powerful minority. But a minority. We have to put aside petty differences and fight the real enemy. Left/right arguments about how to spend the country's money can wait until we have won the larger fight.
EU membership shackles our politicians so that rapid, disruptive change is impossible. The fascists want to break those chains so that they can take the country in a radical new direction. We need to ensure that the brakes stay on, so that politics can continue to reflect a broad consensus, rather than be captured by a radical faction. In the past, before the EU, local government helped to constrain Parliament. But shires and boroughs have lost pretty much all of their power. It's true that the recent devolutions to regional governments have replaced that a bit, but much of England is still ruled directly from Westminster.
Within the constraints of EU membership, Corbyn stood to represent a strand of opinion who deserve a voice. As PM, he could have steered politics in a different direction, whilst being forced to compromise with everyone else. But he has a long history of sharing the fascists' frustration with the EU. I've been watching their forums, and they are all quite clear that he is one of them. He wants to empower Westminster, so that the next Labour govt. is free to usher in a radical socialist utopia... It's fools' gold. Firstly he's not going to get to use that power - he's the leader of a minority, of a minority, of a minority (radical left < Labour < non-fascists). Secondly, even if he somehow won power and imposed all of his well-intentioned changes, he wouldn't carry the rest of the country with him. Change needs to come slowly, and have a broad base of support if it's to stick. It can be nice to imagine what you would do as a dictator, but the truth is that authoritarian rule is always bad.
Labour party MPs seem to understand that. From what I've read, this revolt isn't simply disgruntled Blairites. Many of his former staunch allies are also adamant that his time is past.