I understand your point. However, we could continue that on to say that there is probably nothing IN LIFE that is not debatable. Anyone can claim anythng. Let's say I say something like "Mt. Everest is that tallest mountain n the world." And someone can say, well, no, when I look at pictures, I think Mt. Kilimijaro is the tallest. And I can say, well no, it's a fact and not debatable. The other can say, yes, but how do we know that the equipment they used to measure it was correct? That would lead to a tiresome searching of all the records about equipment was used to measure, was that equipment working correctly, did the people who use it use it correctly, etc. etc.. We could debate that for years. The truth is that it is an accepted fact that Mt. Everest is that tallest, and so that prevents the need for someone to constantly have to take months out of their life to go research every single accepted fact which someone else refuses to believe.
The same idea can be used for behavior. There is an accepted "norm" and accepted standard of how human beings GENERALLY behave and react in situations. Now, there will always be a few that don't react in that way, that doesn't mean that we should change our view of the accepted "norm." Because otherwise, as in above Mt. Everest example, for each situation, we would have to stop and go back and research, okay let's find a statistic of how the majority of people would behave in this situation.