Emotions are a form of social communication. Laughter communicates that all is well, we are safe. Fear communicates danger--look out! Expressing the wrong emotion breeds confusion.
Why do we accept that you will trust your judgement over science when merging into traffic, but criticize parents who trust their judgement over science when withholding vaccinations from their children? Why is merging into traffic something that requires personal discretion whereas, with vaccinations, science trumps personal discretion?