"And you can raise that canard again, forgetting that the Crusaders of the First Crusade were treated as sub-human by the Easterners."
Well...your point is? In my family, the tradition is that the first Crusade was filled with foul smelling, filthy, uneducated drooling louts who really made quite a mess. Confidentially, I hear they actually bought their own silver. Tich, tich! How would you have had us treat such creatures?
I am sure that in each and every instance there were good reasons why Roman Catholic powers sided with or cooperated with the Muslims against the Christian East, and I really don't care that they did -- what each country and what the Vatican does is its own business.
But surely you can understand why Orthodox would take with a grain of salt the idea that the Roman Catholic world has a visceral desire to side with Orthodoxy against Islamic expansionism.
The interpretation that Orthodoxy has of these overtures is that the real goal is political unification of the churches, and that "a united front against Islam" is a tool to achieve that, rather than the reverse, as you suggest.
The East, I am sure, will be more than happy to have the West (of which I am also a part, regardless of my religion) forcefully take on Islamic expansionism, after having borne the brunt of it for centuries. Just don't try to convince anyone that sending Catholic missionaries into Orthodox countries to proselytize is somehow going to help Orthodox countries in their struggle against Islam.
There are plenty of things we can work on together politically: opposing abortion, opposing gay marriage, supporting home and church education, supporting Christian charities, and yes, opposing Islam and the terror it produces. There's just no reason that we have to share a common chalice for us to do all of these things with great effectiveness and in a spirit of mutual Christian love.