Do you seriously believe 2.5 million muslims will leave facebook? I doubt that very much. Just as you are upset if one of your questions is removed without just cause, then these muslims are aggrieved that these facebook pages have been censorred
It is interesting to note that the Prime Minister is unable to get a page removed, yet a bit of Spam can do it.
Most of the time, unless they are posting Islamic stuff, you wouldn't know whether the people of Facebook were Muslims or not, or from other religious background or none. It does seem that the pages which have been taken down were contravening Site Rules, not because of their Islamic content, so surely all they have to do is take out the offensive spamming element and then reinstate them. Everyone happy.