Those sects would be effectively irrelevant in US politics, which is the primary difference and why the comparison to evangelical Christianity is pertinent in politics. There mainstream and most powerful sects of Muslim America are supportive of gay marriage, otherwise we'd see a much lower average. There are many sects of Christianity that have higher levels of support, but none are as influential or politically powerful as Evangelical Christians, which admittedly is more of a political identify than religious identity at this point.
Again, I'm not sure how there's any debate when saying that by and large, Muslim Americans are more supportive of gay rights and issues than a key Christian denomination like evangelicals, white or otherwise.