Something that I think is being elided too freely in this discussion is the difference between being broadly or even powerfully convinced that Badiou has certain things right, and thinking of oneself (or wishing to think of oneself) as a "militant of a truth" in the sense he establishes. There has been no Badiou-event; Badiou's philosophy is not a truth procedure. Whatever else it is to be a "Badiouvian" (and I am unconvinced that the organisers of the Birkbeck conference were anything of the sort), it is not incorporation into the body of a truth.
You keep saying "truth" as if simply uttering this is the final word on any political subject, and if people only had more "truths" they'd be more politically viable.
People already have their petty little opinions and "truths", and there are thousands and millions of organizations and institutions and political militias and so forth that believe in their "truths" enough to do really stupid, selfish, pig-minded shit in order to either get what they want or make a spectacle trying.
The problem is the world is a complicated place. It's often the case that even the most ABSOLUTIST truths have little bearing on what's actually at hand.
Scientists, when they're wrong, and the data proves it, move on. Dogmatists don't. That's the difference, and that's why scientists keep making things and dogmatists keep making genocide and societies that collapse within 50 years.