The good etymologists at OED help us to know ourselves: A conspiracy theory is 1) an explanatory proposition that 2) accuses two or more persons, a group, or an organization of having caused or covered up, 3) through secret planning and deliberate action, 4) an illegal or harmful event or situation.
I find this definition interesting because it aptly describes an historian, economist, or political scientist who proposes, in an academic journal, a theory that explains how a group or organization might cause or cover up, through secret planning and deliberate action, an illegal or harmful event or situation. We professors submit articles like this all the time. Isn’t that worth studying and debating?
Frankly, the term is a propaganda meme used to discredit anyone, anywhere, in quick blunt fashion.