The Christian religion took nearly 1800 years from its beginnings to reach the Enlightenment, when it was reinterpreted to a human-centred concept, where happiness, contentment and fulfilment were seen as the focus of life, and individual life and opinion were respected. Prior to that people were executed by religious courts for blasphemy.
The Islamist extremists need to reinterpret their religion in a similar way. One way they can be persuaded to do that, is for them to see that when the Koran instructed them to kill non-believers and conquer their lands, the world was not multicultural and mixed together. Lands were either 100% Moslem or 100%% non-Moslem. the only way to spread the religion was by conquest, it seemed.
Today Moslems are allowed to come to Britain and the West and preach their religion, and mix together with non-Moslems. They do not need to kill non-believers to gain access. In fact doing so will damage their religion as the West is forced to take measures to defend itlelf by invading the Moslem lands where the aggression is controlled from. Their actions could be causing a loss of power to Moslem countries and damaging their religion, which is not what the Prophet intended.
Their aggression could eventually cause the Prophet to be rejected from western lands if they persist with killing non-believers. Why not focus on converting the west by peaceful means as the opportunity is there without the need to kill people? The situation was not forseeable so long ago, and the texts need to be reinterpreted for the modern world, if the religion is to thrive.