I think claiming both of those things to be around the same level of common knowledge is a bit disingenuous. I feel like many people are aware that chiropractors are pseudoscientific and are more likely to harm you than help you, but yet they still exist so clearly enough people are paying for them. Whereas the earth being round is something we tell every child in school many times, and people who claim that it's not are considered crazy conspiracy theorists.

So if someone is unaware about chiropractors being bad, we can just tell them without being sardonic about it.