The Labour Party grows from the Left. It shrivels when it settles down at the Centre.
If the Labour Party is not a protest movement it is nothing.
For long periods it has failed to win elections. When it has won an election with the spirit of protest still strong in it, and harnessed it to the task of governing, it has achieved something.
Winning elections is often a matter of luck. If the Centre Ground PLP, which has boycotted Corbyn, was lucky and won an Election, it is a virtual certainty that it would just serve its term in Office in a way that was indistinguishable from Tory government, except to the people who have Government jobs for a few years.
Posted as a web page and also available as a PDF, Labour Needs Corbyn (pamphlet)