> There aren't any unknowns waiting to be discovered. The mechanism is fully-understood and easy and safe.

I am sure many people felt that we had figured it all out w.r.t. planet motions etc. with Newton's law of physics :)

You are mistaken if you think I am anti-vaccine or something. I merely tried to point out that there are always unknown unknowns and that we should remain cautious when it is people's health that are at risk.