I have conversed (by email) with David Horowitz for over ten years. He is committed to religious liberty and opposes Marxism in general (which is why he was there). He would oppose an imposed religion, whether Islam or Judaism.
However, as I have read his writings for over a decade (and before he started FrontPage Magazine), I would say that he is neither seriously religious nor does he understand the original design of our Constitution as PRESERVING the rights of the States to institute an establishment of religion should the people so choose. The reason is simple: there really are civil laws mandated in the Bible, with penalties for crimes, a mandated Sabbath, instructions for civil administration, etc. ALL of which would effect State and local laws. For the people truly to have the liberty to live as their religions dictate, they would have to be free to institute such local laws. Horowitz would oppose that as an imposition on everybody else, just as most people would today.
The Founders saw Federalism as a solution to that problem, where people could institute local laws to serve their preferences. If a minority didn't prefer a religious administration they could simply move to where the local laws befitted their secular preferences. As we have all seen, the system has been used to enact secular uniformity by force. There is nowhere today a person can move and live where local laws meet literal Biblical demands, particularly in Lev. 25. We thus have no liberty to witness or perfect a working model of Judeo-Christian administration. There are consequences you know.
The Liberal-Muzzie Alliance reminds me of the Hitler-Stalin Pact.... you never know which one will turn on the other first.
Horowitz stands against islam. Every day.
You know where to look for perfection.