This is rather silly, self-serving, stuff from Owen Jones. Labour and the Conservatives will both be threatened by a new Party - but only if they don't speak to those who feel disenfranchised. That is, and should be, how democracy works. 
If Labour chooses to be led by the divisive Corbyn, a man who can't muster the support of a quarter of voters, even in a head to head with Theresa May, it is vulnerable. That's not assertion, it's just maths.
It's not rocket science: FPTP demands pluralism. So why not reflect on why Labour is vulnerable? Instead Owen (again) pours anger and ridicule on the unbelievers. And he generates the very division that makes a new Party likely. And he becomes a cause of that he seeks to prevent.
