The scientist was sued for libel for making statements of fact about chiropractors. (Remember that in the UK the fact that you're saying something true is not a defense against libel. This is one reason why people seeking to sue for libel try to sue in England.) But that was overturned because it was ruled that the scientist was making a statement of opinion, not fact, and therefore could be held to a more generous standard.
So scientists are allowed to comment about pseudoscience so long as they are clear that they are making statements of (supported) personal opinion rather than statements of fact. As messed up as the USA can be, I'm suddenly glad I don't live in England.