Jeremy Corbyn and the median voter theorem

The half million voters of the British Labour Party have decided that the median voter theorem is wrong. Perhaps they are right, but unfortunately that does not guarantee that they will succeed in winning the next general election, if Mr. Corbyn is still the leader by then. The median voter theorem says that under some assumptions, in an election with two relevant political parties, both will converge by presenting that platform that best satisfies the preferences of the median voter, the one that has half of the population at her left and half the population at her right. Then both parties have equal chances of winning the election. Although reality departs from the assumptions of the theorem in some relevant ways, the fact is that many democracies, including the British in the last decades (not in the times of Thatcher), shows a tendency for the big parties to converge to the center. Now the Labour Party has chosen a leader that is closer to the extreme left than to the center. He looks a decent person, and I am sure that his voters (which include many new party members in a well organized strategy from agents initially external to the party) have the best of intentions. The words in Mr. Corbyn's acceptance speech included many references to trade unions and to passions. I understand that his expectations are that a passionate enlarged party membership will mobilize the vote to defeat the conservatives on left wing causes. His critics claim that the average voter in the UK is not that left wing and that the difference between the preferences of the half million Labour party members and the millions and millions of potential voters is huge. One thing the median voter theorem did not solve is how to give incentives to citizens to create and maintain a political party if this party at the end defends the same policies as the rival party. For a group of citizens to have such an incentive, there must be some difference at the end so that they capture some ideological or resource benefits (beyond the rents from being in office for a very small minority). To me, the challenge remains how to encourage a core base of voters and members without discouraging the mass of voters. Beyond this, there is nothing much exceptional in the election of Corbyn, which belongs to a decades long debate in the left between radical and moderate forces, a debate that will continue perhaps forever. Depending on economic crises, leaders' personalities and other factors, in some periods the radicals will dominate, in others the moderates will prevail.