The odd thing is, I often have trouble getting students to disagree with me. For example, whenever I teach Marx, I set aside some time to have a discussion of what's wrong with his picture. Almost invariably, the students are pretty quiet, and then I'll have to tear into him, which will involve some 'odd' criticisms (criticism from the left, academic criticism rooted in civil society, a critique of disciplinary society, etc.). It's almost as if they wish me to fill them as vessels.
ebola
Or they're trying to figure out what "Alien Nation" Marx was referring to, and why he never talks about the aliens themselves.
From what I recall of teaching, at times the best thing to spark a discussion if I were facing a silent room would be to introduce a single, easily understood, claim of the author, and then explain it anyway, and then point to a student and ask him to come up with criticism of it. And then point to another and ask for a defense, addressing the criticism of the first student. And so on. Oddly enough students would usually get attached to whatever position they were assigned to criticize or defend, which helped.
If it were a small enough class or section, I would break them into teams, one side for, one side against, and simply prod them into arguing with each other.
Once there's some initial movement, they seem to lose reluctance to speak and engage. Natural competitiveness and sociability take over as they react to each other. And along the way, I can shape the discussion, add in additional arguments by the author, and so forth. If it goes well, they're still arguing when they leave.
IMHO, frequently if a group of students are unwilling to give their own opinions, 1) they're hung over, 2) they haven't done enough of the reading, haven't thought much outside of class, and are still trying to digest what they just learned in class, or 3) they are simply in awe of the teacher's brilliance, charm, and physical beauty.