Normal is a subjective term. It implies a mean average of a sample. It's an argument from consensus and a weak one at that. What one determines as normal only illustrates a structure of biases based on personal experience. I take heed of it in the same light as anecdotal evidence.

I think that we are normatively constituted.

If so then to ask if "Is normativity a valid point of reference for backing arguments?" involves a circularity, since our language in itself is normative. The words and the meanings we attach to those words have historical meanings, and if we don't follow language's normative structures then we risk being misunderstood.

"Life and existence are necessarily and in part defined by approach and attainment. That truth, in all cases, excludes normal life and normativity as necessarily true conclusions."

Life and existence are necessarily contingent and they are defined by our being in the world. There is no such thing as absolute truth, or necessary truth ( to assert these is to assert god).

What truth there is, is all about normative roles we assume in life, all the rest is conjecture, based on premises which can be affirmed or denied.

This is a conundrum question because everyone has a slightly different perspective of what normal is. Example putting the toilet paper on a roll putting it over the top might seem like common sense because it is easier to spin towards you from the top. Another might think that pulling it from the bottom makes more sense because it is easier to pull. Then another might not like it on the roller at all because it is a hassle. Then another might not use it at all because they prefer the bidets. So what is normal, an agreed upon choice? So who`s choice has a more perceived efficient way of accomplishing a goal?

When people use the word "normal" they most often mean "typical" or "expected". There is no automatic virtue in that. Quite often it cloaks mediocrity and unimaginitiveness.

Norms vary in their usefulness as touchstones for how one "ought" to act. It's better to have considered and defensible reasons for why you do what you do. Better, but harder.

Of course norms are a shortcut that people do use. My wife has a favorite exclamation, "who DOES that?!" when someone does something she thinks particularly egregious. But I keep telling her, it doesn't matter who does or doesn't do something or frown on something, it matters if its right or wrong to some reasonable intersubjective standard.

Guess if they are happy with all C's then the norm is good enough for them but not for us.

You may need to further clarify.