Right-wing extremists in the US are promoting far-fetched suspicions about vaccines, and even the former doctor whose fraudulent claims started those suspicions.

When parents act on these fantasies, real children get real diseases.

It is wrong to censor the statement of views on the grounds that they are mistaken. On this, I actually agree with Zuckerberg.

However, when you are presented with claims that a conspiracy is stifling the truth, consider whether the conspiracy is plausible.

It takes a lot of money to corrupt lots of scientists and officials. Companies that sell products that many people use every day can afford this — products such as tobacco, sweets, fossil fuels, and opioids.

Oil companies have enough money to corrupt institutions such as the Museum of Natural History and WGBH-TV.

How many packages of sweets are sold in the US every year? My quick estimate is 400 billion, but it could be much more that. There's a lot of money available to corrupt the institutions that ought to be adopting policies to help people resist sugar.

Telecommunications companies have enough money for this (look at the network neutrality battle). A commercial movement backed by billionaires can also corrupt people and institutions. For instance, charter schools are backed by billionaires.

How many doses of MMR vaccine are used in the US every year? I estimate around 6 million. It is a substantial business, but not enough to make a billionaire. It is not plausible that these manufacturers can corrupt a large number of people and institutions.

What kind of conspiracy can a small business set up? Only a rather small conspiracy. Andrew Wakefield's fraudulent paper, which first claimed that MMR vaccine did harm, was a conspiracy of that sort. It fooled a part of the scientific community for a while, until more investigations showed the claim was false.