The idea that religion qua religion cannot be bad (unless it's Christian, of course) does predate PC MC (even as Western anti-Westernism began to develop before PC MC -- even before Leftism proper).
More often than not in my readings of writers of the past mentioning Islam, they regard it, and frequently describe it, as a religion. However, the further back in time one goes, the more is this acknowledged religion condemned -- though not uniformly by every critic writing about it, and it's not unusual even in pre-PC MC eras to see writers afflicted with the "well there are good aspects to Islam as well" tic.
But one thing history teaches us in this regard is that many people had no problem largely condemning Islam while also regarding it as a religion. So I don't think this is an insurmountable problem; just one more difficulty to add to the rest.
Basically, before the races begin, we are in our time debilitated by certain handicaps imposed upon us by our surrounding culture:
1) Islam is regarded as a religion -- indeed, a "world religion" spanning the globe and having a rich inveterate history, and impressively populated by some 1.3 billion adherents.
2) The sheer quantity of adherents and their geographical extent in a global diaspora also inhibits too much criticism that veers toward "generalizing" (or that even smells like it might veer that way).
3) Our generally held and cherished principles of "Don't paint with a broad brush" along with "Innocent until proven guilty" exert much influence.
4) Then considerably augmenting the power of #1-3 is the central principle of PC MC: Reverse Racism. The vast majority of these adherents are perceived to be "ethnic" -- indeed, of various flavors of ethnicity, consituting a veritable tapestry or mosaic of charmingly non-Western colors and patterns of skin and garb and exotic cultures. And this isn't a stretch on the part of PC MCs: it's not like they have to twist reality into some strange counter-factual fantasy: 9 times out of 10 when you look at a Muslim or group of Muslims (or a sea of Muslims devoutly praying or hatefully protesting or fanatically fighting), they look ethnic -- and this unremarkably reflects the historical fact that Islam spread its vast imperialism largely throughout what later came to be known as le Tiers Monde (the "Third World"). This is an advantage for the other team, and a handicap for us, because PC MC, which is dominant and mainstream and enjoys all the advantages which sociopolitical mainstream dominance endows, is centrally wired to favor and privilege ethnic minorities -- and because of their violence, this Designated Ethnic Minority of Muslims has elbowed its way to the top of the heap of Ethnic Minorities (since, as the saying goes, "the squeaky wheel gets the grease" -- and this particular wheel is squeaky with a terrible vengeance, portending a global train wreck nobody seems to care to stop, let alone notice, except those few of us who have to stand by and with growing horror watch it unravel).
5) Finally, the other central principle of PC MC -- excessive self-criticism of the West -- in its turn gives an added jolt of caffeine to #4.