We simply do not know who drives the failed agenda in the Labour party.
Is it Unite? Momentum, the hard left crazies? The present crop on offer in the leadership contest provide little to impress. The fact that Corbyn is allowed to remain as leader clearly demonstrates the fractured state of the party. For as long as he remains without public condemnation or censure, the party is heading for oblivion.
The recent election made it very clear the electorate will not accept any part of what the Corbyn cult offers. Labour has   an upcoming fight between hopelessly failed ideology and pragmatism. The party is in a state of paralysis, surely no other explanation can justify Corbyn continuing to be leader.
Unless the party reinvents itself it will never hold power again. The message of unelectability was enforced by the mass migration of labour seats to the Tories in the Labour heartlands. Betray your electorate-pay the price! Simples!
As for "winning the argument"-words fail.
Such a level of delusion surely demands sectioning, for public protection.