Or drinking a glass of wine every single day.

> Why is it so easy to cast doubt about them?

Because people will say just about anything if you pay them to say it, and they will keep saying it for as long as you keep paying them.

This feeds into people reasonable assumption that if to different people are saying different things these is some doubt about the issue.

> Why is it so easy to cast doubt about them?

The entire vaccines cause autism thing started as a disinformation campaign against the MMR vaccine in order to sell an alternative (expensive) 3 part vaccine and to win a lawsuit. The media gave the original paper huge coverage without actually reading it and it took many people a lot of work debunking and discrediting the author before he even lost his medical license.

You never read "We got tricked into spreading BS" on the front page of a newspaper.

Thalidomide might be what you're thinking of. Didn't realise until now that it wasn't approved in the US until the risks were well known. But in the UK at least "thalidomide was (supposed to be) safe too" is an easy argument you'll hear fairly often.

>... a subsidiary of Distillers Co. Ltd (now part of Diageo plc), marketed thalidomide throughout the UK, Australia and New Zealand, under the brand name Distaval, as a remedy for morning sickness. Their advertisement claimed that "Distaval can be given with complete safety to pregnant women and nursing mothers without adverse effect on mother or child ... Outstandingly safe Distaval has been prescribed for nearly three years in this country."

>Experts estimate that thalidomide led to the death of approximately 2,000 children and serious birth defects in more than 10,000 children, about 5,000 of them in West Germany