Human behavior changes radically based on context, culture, and age. And every historical period has had different expectations for human behavior. Given the flexibility of the concept of “normal,” do you believe there is such as thing as a “normal” human being?
In dealing with “normal” as well as “human nature” it is important to distinguish between the individual and the group.
I have found over the years in my interactions with others that at times there is an “appeal to normal” in other words the person might say something like. “That’s just not normal behavior”, especially when it refers to a behavior that we don’t like. My take on that is that if we care about the other person we need to try to understand the roots of the behavior for that individual situation rather than trying to dismiss it as being abnormal.
On a wider statistical level, “normal” can be more useful especially when designing something like signage in a train station. Establishing conventions for behavior and for surrounding infrastructure is helpful in navigating our world. It is important to understand those conventions so that we can all interact smoothly. But it is also important to realize that those are very broad guidelines that don’t apply on an individual basis.
I think you may be conflating “normal” with “norms.” We all function best when there are norms to go by–that is, a set of rules and expected behaviors for various situations. But those norms vary by location, time of day, group of people, geography, and much more. For example, our norm is to provide restrooms in restaurants, and to provide expected signage so that users can find the appropriate location to relieve themselves. The norm in the woods, however, is to simply step behind a tree. But establishing conventions isn’t the same thing as establishing what it means to be a “normal” human being. I also think that “abnormal” behavior is usually more than “behavior we don’t like;” it’s behavior that goes against the norms. So, for example, a woman in the man’s bathroom is not “normal,” though of course it’s perfectly normal for a trans man!