Bagpuss: Half serious, I know, but let me give a serious answer nevertheless.

If the placebo action argument is taken serious as I think it should then knowledge can have adverse effects. There are other examples in which knowledge can have adverse side effects, for instance in the enjoyment of a conjurer if you know how he does it.

I only can say that I think that the benefits of knowledge outweigh the adverse effects.

Now for the less than half serious response: I even have the effect that when my doctor gives me a medication and tells me that it works I surrepetitiously think perhaps I'm only in the placebo control (and of course he wouldn't tell that to me). Now I know that under some conditions real medication can have a weaker effect when you tell the people (wrongly) that they are in a placebo control group (that's a very interesting control group for many reasons). Could it be that the mere thinking that I might be in a placebo control prevents the benefit from the usually good medication in me. But then, since I know that, perhaps the this effect doesn't happen....

Sometimes I enjoy twisted thinking

Wolfgang