@elit I don't think anyone is really condoning or recommending the stabber's course of action, we're simply stating that we are more disgusted with the actual parade in which multitudes desecrated the name of hashem than the stabbing which was one zealot who took things into his own hands. Furthermore, as per the title of the thread, the stabber is just as Jewish (actually much more so but whatever) than the gay protesters. What this Rabbi did doesn't contradict this sentiment, and even if it did, it's still a total non issue. He's not Moshe Rabbeinu that we can't argue on him, nor is he even one of our great poskim. He's a rov, and probably a talmid chacham, but he knows the same sources as anyone else does. No worries, I'll go into Meah Shearim and I'll find you a Rav who holds that the stabber was mekadesh shem shamayim and is a big tzadik if that's what you want.
ETA: I also hope you can differentiate between political rabbanus and real rabannus. If the Israeli chief Rabbinate camr out with a statement about this it would as much as Obama deciding on a matter of Halacha-purely political. I don't think you'll see Rav Chaim Kanievsky, for example, visiting these people, regardless of what he holds on the matter, given that he's not involved in politics. So what would be appropriate is perhaps quoting me a source in Halacha on the matter, not pointing to political showmanship as proof of the Halacha.