I don't think it's about stifling debate. It's about one man doing some dodgy research, the media running riot with it and a shitload of people getting scared. To echo another thread, Wakefield doesn't have the grace to admit he was wrong even when the evidence says he was and continues to perpetuate his views with the support of a small but vocal minority of parents of autistic children.

The final chapters of Ben Goldacre's excellent Bad Science are about the MMR scandal. They make for very interesting reading. Goldacre, of course, is an advocate for evidence based science.