Part of this is no doubt that everybody likes rooting for David against Goliath, and its no skin off their noses if we get bruised.
Part is systematic. The worst believer is better than the best nonbeliever.
It is an article of faith that even the most wicked believer is in a different and better relationship to God than the most virtuous unbeliever. Here understand unbeliever as one who has rejected the revealed truth. The merely ignorant are in a rather different class. Because your relationship with God is infinitely more important than your relationship to anyone or anything else, if follows that even a wicked believer is better before God than the most virtuous person who rejects God. Note that there is a slight difference between my statement and the title.
While a Christian might object that you can't hate your visible brother and still love the invisible God, Christians also hold that believers are better before God than rejectionist unbelievers.
There is no point in trying to challenge this doctrine. That a supernatural relationship is established between God and His worshipers is central to Islam, and to Christianity, and a number of other revealed religions as well. While several Christian denominations deny this, close examination shows that they have departed from orthodoxy in many other particulars as well and do not reflect traditional Christianity.
Who is competent to judge who is a believer and who is not? Christianity and Islam nominally provide different answers to this question--after all, Jesus warned that not everyone who called Him Lord was one of His; while anyone who pronounces the formula is Muslim. In practice when clerics dominate we tend to see the same sort of assumptions in both--either you see an inclusionist "If you do the basics you are a real zzz" or you see a heretic-hunting "If you don't do the details you're not a real zzz." In either case the clerics feel competent to judge, and everyone else can follow their lead. This attitude isn't quite as unjustifiable as it might appear, since the proper relationship with God ought to properly order the rest of one's life (sooner or later), and this can be dramatic. We can easily distinguish between Mother Theresa and John Wayne Gacy.
Still, this judgment can look like a usurpation of God's prerogative.
What are the practical consequences of the attitude that a believer is better before God than an unbeliever? First notice that if I am competent to judge who is a true believer and who is not, then I can safely say that a believer is better than a unbeliever. Second, the more tightly coupled all aspects of the law are, the larger will be the differences between believer and unbeliever. Commonly a believer's testimony carries more weight than an unbeliever's, who already shows a disregard for the Truth. It just gets worse from there, with greater and greater disabilities applied to the unbeliever. Sharia notoriously couples all aspects of law, but the lack of divine authority to oppress unbelievers hasn't always hobbled Christians either. (Of course in Hinduism, where it is impossible to change your religious status, the restrictions on non-Brahmans enforce a permanent and particularly noxious caste system.)
We have a secular society for a number of reasons, including the rise of atheism/secularism, the ascendancy of philosophies that despair of finding absolute truth, a history of bitter experience of religious wars, and a little sentence of Jesus' about giving Caesar what was his and God what was His. The secular society shows some great advantages, even though it has some shortcomings. In fact our society is very aggressively materialist and anti-religious, unless those religions are willing to become materialist and un-dogmatic. This doesn't seem to endear us to Muslims.
I take it as given that a materialist or un-dogmatic religion isn't worth the water to flush it. Attempts to make Islam un-dogmatic I believe must fail at the best, and backfire at the worst. Orthodox Islam is always going to hold that a believer is in a special relationship to God.
At the other end of the chain we find that Islam so tightly couples all aspects of law under divine authority that it seems inevitable that unbelievers must be treated worse than believers.
I think the weakest link in this chain is the assumption that a human can judge if another person is a true believer. If you lie while pronouncing the Muslim formula, are you really a Muslim? Is rebellion against the laws of God kin to apostasy?
These subtle points are not useless speculation. We want Muslims to despise evil-doers who injure infidels just as they despise evil-doers who injure Muslims. The more they blindly hang together against the infidel (us), the more cover and scope the bin Ladens have. They should not usurp God's prerogative of final judgment, and restrict themselves to what a human can judge. A little uncertainty about who is honestly Muslim seems compatible with some of the hadiths I've seen.
We need to persuade them that this is Islamic and pious.
We would like Muslims to have the benefits of a secular society (preferably without the evils). They won't accept it unless a secular law is a logical consequence of Islam, or at least not in conflict with it.
We need to encourage them to find the way.
Where can we find scholars willing to study Islam and its expressions who are unafraid to challenge foolish implementations? Perhaps we can't find enough left in the West, but maybe there are some bold souls within Islam willing to ask the loyal but hard questions.
