As for understanding where they are coming from: I cannot speak for Lacan (who certainly said stupid things, but who hasn't), but Bruno Latour has done some fascinating anthropological work on science. Reading "Laboratory Life: The Social Construction of Scientific Facts" changed my vision of science. Contrary to what Bricmont claimed in one of his article about the affair (French title: "La vraie signification de l'affaire Sokal"), Latour has never claimed to my knowledge that science was just a social construct, but rather that the scientist activity cannot be thought independently of its social environment. When Bricmont says in the same article that "Comment peut-on soutenir sérieusement qu'il n'y aucune raison empirique de croire que le sang circule, que la Terre tourne..." (my quick and rough translation: could one really claim that there is no empirical ground for blood circulation or Earth rotation), that's disingenuous.
But what bothers me the most in the whole affair is that for people who claim defending science and the scientific method, they prefered the polemic, uncontrolled manner rather than an actual experiment to prove their point. That's rather ironic.
I'll admit I'm biased here. Latan, Irigaray and co. sound like a bunch of charlatans to me. However, you're suggesting that I should try "understanding where they are coming from". So please explain to me where Irigaray is coming from when she suggests that fluid mechanics is neglected because "the problem of turbulent flow cannot be solved because the conceptions of fluids (and of women) have been formulated so as necessarily to leave unarticulated remainders."