Good cannot have a productive dialogue with evil.
But man contains both good and evil. The Pope is not attempting to dialog with the evil that lies at the core of Islam, but is rather appealing to the vestiges of goodness within some of its aherents. Although my knowledge of the Koran is superficial, it does seem that Islam, unlike Christianity and Judaism, is incompatable with reason.
Therefore, the seeds of reason can weaken Islam's death-grip on at least some fortunate souls.