I use a similar approach, and it usually works. Make clear that you don't think you're holding the truth on the subject, whatever it means, but only that the information in your possess led you to the conclusion youre presenting. Manifest curiosity for the position the other side is expressing, even if it's cached, and even if you heard similar versions of it a hundred times before. Try to drive them out of cached mode by asking questions and forcing them to think for themselves outside of their preconstructed box. Most of all, be polite, and point out that it's fine to have some disagreement, since the issue is complictaed, and that you're really interested in sorting it out.