I'm sorry. But:
1. Even if hatred of homosexuality were intrinsic to Islamist and Christian fundamentalism, the fight against Islamic fundamentalism isn't about homosexuality. It's just not and no matter how much you care about the issue, it won't ever be.
2. Islamic fundamentalism and Christian fundamentalism aren't the same thing. They can both be "bad" but that doesn't mean they are the same. Depending on what you mean by Christian fundamentalism, I don't think it's bad. I certainly don't think it's bad if you go by Andrew's expansive use of the phrase. But even if I did, I would recognize some important differences between the two. Like: Christian fundmentalists have not constructed a grand theological construct to justify mass murder in the modern era. No followers of Jerry Falwell are suicide bombers. This is not a minor distinction. Christian fundamentalism gave birth to the Protestant reformation, individual liberty, the American nation, the modern American university, and the like. (bolding added) This is not a minor distinction either.
Christian fundamentalism grew out of the British and American evangelical revivals of the late 1800s, and the term itself didn't come into wide usage until about 1920. I suppose that one could assert (without bothering to demonstrate, as Jonah so often does not) that Protestant reformers were "fundamentalist" in their interpretation of scripture, I would strongly disagree, but in any case this would be applying a distinctly modern concept, as religious fundamentalism has always been a reaction to modernization, to events which predate it by almost four centuries.
The idea that you can square the political philosophy of the American founders, who, after all, gave us a constitution with no mention of the divine other than the words "Year of Our Lord" in the dateline, a constitution which specifically stipulates that government should "make no law respecting an establishment of religion", with Christian fundamentalism, which is defined by an insistence on scriptural inerrancy (the belief that every word means exactly what it says in English, translated from the Latin, translated from the Greek, translated from the Aramaic and Hebrew...), or that the former could have conceivably arisen from the latter, is flatly ridiculous. Indeed, Christian fundamentalism is in many ways a revolt against the secularist principles enshrined in the U.S. constitution.
This is what Christian and Islamic fundamentalism have most in common: an open hostility to pluralism, to the idea that government should operate as if the ways and beliefs of others were as legitimate as their own. In this sense, Sullivan is right that hatred of homosexuality is intrinsic to Christian and Islamic fundamentalism. The struggle against Islamic fundamentalism may not be "about" homosexuality, just as the struggle against Christian fundamentalism is not "about" abortion. These just happen to be two issues upon which democratic pluralists and religious fundamentalists can not and very likely will not agree, and where the war between the partisans of government by consent and the partisans of government by divine diktat will continue to be fought.
Regarding Jonah's point that "no followers of Jerry Falwell are suicide bombers," I agree that this is an important distinction. For now, Christian fundamentalists still seem committed to using the legal system to force their very particular views of religion and morality on the rest of us. For now.