First, Chesterton and Belloc allegedly did "not delude themselves that all other peoples are just bourgeois Westerners in costumes." Although this sounds good, in fact Cella doesn't make the point that Muslims aren't the same as bourgeois Westerners in the important respects. Don't we on average enjoy the comforts of life much the same? You find sects and individuals rejecting bourgeois values throughout the world -- Mennonites in South Ontario, for example. And, you find astute traders and practitioners of commerce (bourgeois) throughout the world, too. Cella's argument is that the Muslim population cannot be understood as having the same motivations as Westerners, but this argument will lead to a greater rift and distance rather than greater understanding.
Next, Cella argues that our modern values of tolerance and plurality are "bluster" and "narrow". I don't think that's right. Although I agree that tolerance can harmfully take the place of judgement -- I don't tolerate a murderer, for example, I judge him -- I still think that tolerance is a virtue. It also seems pretty obvious to me that our increased modern tolerance is more than simply bluster, and that it isn't very narrow either. (It also seems self-contradictory to both argue that our "bluster about tolerance" is narrow and also argue that our tolerance goes too far.)
I won't go through the whole article looking for these kinds of things but finish by pointing out what first started to make me feel uncomfortable. Cella's basic point of admiration for Chesterton and Belloc is that they felt the heresy of Islam was dangerous. This is, as Cella admits, a deeply unmodern viewpoint and I'd prefer it stay that way. Chesterton and Belloc wouldn't have considered Ireland's Catholic Church as heretical, yet that didn't stop it from imprisoning young women and profiting from their labour as recently as the 1980s, as portrayed in The Magdalene Sisters.
Perhaps we do need to take into account the power of faith in driving people to suicide bombings and enslavement of others. However, we do not need to approve, nor does it help for some of faith to accuse others of heresy.