With out placebos, you couldn't run clinical trials for example.

You would also have a huge problem with antibiotics. Most people still think they are the cure all and demand them at every given opportunity. The more use they receive, the more resistant the bacteria they are design to counteract become.

This article was the one I was talking about: http://newsroom.ucla.edu/portal/ucla/first-genetic-evidence-for-why-96163.aspx