In the recently concluded conference on "The Future of Protestantism," a sentiment was made at the end that when persecution happens, there will be "unity" among all Christians. And in the sense that persecution tends to draw people together, that seems true. When a Roman Catholic is on the receiving end of persecution for bearing the name of Christ just as you are, it seems logical that the two of you would forget those "pesky insignificant doctrinal differences" and unite around Christ, or should it?
The question before us remains: "How is a person saved?" The question should not be: "Is the person called a Christian?" We must remember that salvation is an objective reality; one is either saved, or one is not, independent of what I or anyone else thinks. If that is so, then it is vital to know if someone has given us reasons to believe they are truly saved, for it concerns their eternal destiny. Merely changing my mind about someone's status before God is not going to do them any good; it is only God's opinion that counts in the end.
If we come to it in this manner, then we will see that salvation is by grace alone through faith alone in Christ alone. Roman Catholics generally deny this truth, unless they are living in the "mortal sin" of holding on to the "Protestant heresy," which means they are considered by their church body to be heretics. So if those like Roman Catholics deny the Gospel, then they are not saved. Even their suffering for the name of Christ means nothing, as 1 Cor. 13: 3 makes plain that martyrdom apart from love of the true Christ means nothing.
So what happens if, Lord forbid, one day Christians and adherents to various other sects are persecuted together? Then our conduct is not to embrace them as believers, but to plead with them to repent and believe in the true Christ even as they are, perhaps, in the same death roll as us. It will not benefit their souls if we try to pretend that they are saved, so why bother with the pretence under a false front of unity, and instead use the time to evangelize them?
That professing Christians from many sects find unity under persecution means that what divides them was not seen to be anything serious in the first place. If they have united with, for example, Roman Catholics under persecution, then it only shows that those believers do not see the Gospel of Justification by Faith Alone to be definitional of the saving Gospel, which is a sad fact. However one trumpets the Gospel of free grace, if one compromises the faith under pressure, it either shows that one was lying about one's prior beliefs, or that one has no strength to hold on to one's beliefs.