I doubt it was the entire membership because if it was how are these parachuted in Oxbridge graduates selected?
It's a completely democratic process. The constituency Labour Party can select anyone to be a candidate - unlike other parties which only allow selection from the approved list.
but I think that the 172 should accept the will of Labour members and acknowledge that the party has changed
But they weren't elected by the Labour membership. "the people" put their cross in the box next to their name - even though the labour membership selected them to have their name on the ballot in the first place.
All the elected officials I have met respect the mandate they have been given by the people. If an MP defects from one party to another, many constituents are unhappy and a by-election often follows. This is no different.
The Labour Party do not know if their change will make a difference to the way people vote or not. What is likely is that many of those who voted Labour In the past, and elected the 172, will no longer vote labour. They may well be replaced and exceeded by new labour voters. But that doesn't get away from the fact that the 172 have a mandate from the people who voted for them.
the 172 are saying that Corbyn is useless etc and have therefore brought about this challenge to Corbyn just one year after he was elected
well, maybe he is useless! Being popular with the membership doesn't automatically make you good at particular jobs. That's what worries me about the idea of the membership selecting the shadow cabinet. Popularity doesn't always equate to effectiveness. If JC is poor at communicating with the PLP, is. (as you have alluded to) unable to influence members effectively enough to eliminate poor conduct on their part, has an abrasive manner that makes him challenging to work for, why shouldn't they challenge him to see if there is someone else who can do the job.
If you and your colleagues had a boss that the customers loved, but was a nightmare to work with, wouldn't you all band together to get rid of the, if you could?