There's a bit of a distinction between a false presupposition and a false entailment or implication - if you had asked "have you stopped beating your wife?" I'm not sure where on the scale from 0 to 10 I would best answer. But yes, I think I answered both of those with fairly low numbers as a result of the presupposition I think is false. I tend to believe the EMH, at least in some weak forms. (I don't know if you read Crooked Timber, but John Quiggin there has recently had some good posts discussing stronger and weaker forms of it.)

Especially since it gives me sufficient reason not to bother with trying to play the market.