I never heard of Urban corresponding with Muslim rulers. Are you 100% positive? I can't seem to find anything online either. All of the Muslim rulers were relatively petty at this time. The Muslim world was deeply divided which is one reason the Crusade met with such success.
It's not a matter of relying on theology. Why would they even talk about that assuming Urban ever corresponded with any Muslim ruler?
Whoever criticizes capitalism, while approving immigration, whose working class is its first victim, had better shut up. Whoever criticizes immigration, while remaining silent about capitalism, should do the same.
~Alain de Benoist