My understanding is that "idiot" is an informal and offensive word in English (correct me if I am wrong).
I would like to use an equivalent word or expression that is more appropriate for an essay with written formal English. Could you propose some alternatives?
PS: Note that I am looking for a word to refer to non-specific people or to a crowd. It should be a clear, but polite or formal word, that states one's opinion about a situation without insulting in a vulgar way.
Oddly enough, the word 'idiot' was once a formal term in clinical psychology. Those with an IQ of 0 to 25 were called idiots, 26 to 50 were called imbeciles and 51 to 70 were called morons. All three of these terms have long been considered to be pejorative. They are often used without causing huge offence but would be highly offensive if used in connection with people with learning disabilities.
As you are referring to a group of people it sounds like you are making a judgement call on their behaviour, not their intelligence. Most people wouldn't be offended if you referred to a group's behaviour as 'stupid' or 'idiotic'. Perhaps the least offensive word I can think of would be to say that they were senseless or behaving senselessly.