Stein is(or at least was) a big time pro-lifer, and also made a film against the theory of evolution, so I don’t think he hates social conservatives. I have no idea what motivates him, to be honest. Truly an enigma.
From what I've seen, Stein likes to hammer on things that (according to him) ought to bug people. In the actual article, Stein hits Miller on three counts:
1. Miller's bodyguards roughed up and hand-cuffed a reporter and took his video camera.2. Miller spoke of East Germany as a good example of effective border control.
3. Miller is refusing to answer questions about his past.
Let's grant that Stein may be leaving out context and such ... but if Stein is correct on the basic elements, he's right to be bugged.