In the light of developments over the last 150 years in our understanding of the mind I think it is important to note that an idiot as Mark labelled one who does not learn from data could be further described as a person of low IQ, such as he meant, as well as somebody who is clinging fast to a false datum that contradicts what you are trying to communicate. This person can be otherwise intelligent so does not readily fit within the framework of what we call an idiot. This latter person can be otherwise quite bright, intelligent and rational, just not on this subject.
If you do not know this it can puzzle you as to why some otherwise intelligent people can be so off the mark on a subject.
Then there are those evil people who profit from lies and deceit, like Fauci, Gates, Soros et al.