The thing with history is that it is unprovable, unlike some things in other disciplines that can be proven (physics, chemistry, etc.). There are no absolute truths in history as such, there are only theories based on evidence. We can speculate and come up with theories (aka "tentative" personal conslusions). Hence challenges are absolutely necessary, just like in any other discipline for that matter. Some people see challenges as a very negative thing, and possibly due to personal insecurities they take them as an insult to their intelligence. But challenges are the basis of learning, and everyone who wants to voice an opinion publically must be prepared to be challenged and must be ready to defend his or her theory/opinion.