Remi,
I not only interpret Geni field names differently from you, I interpret the English language differently.
There can be no question as to the meaning of the phrase "maiden name", nor can there be any question as to what the field of that name should contain: it is for the name prior to marriage, i.e. the name at birth (usually, there are a few exceptions).
There can also be no question that Geni anticipated the preferences of people like you, which is why they they have an option:
* Maiden name instead of last name
If your idea was in any way correct, then you are claiming that Geni created an option that effectively reads:
* Birth name instead of birth name
Obviously, that is NOT what they did, so regardless of your assertions about The Way It Should Be or The Way Every Program Does It, your position is incorrect.
What IS obvious is that Geni anticipated people like you whose purpose is primarily the production of pedigrees. Which is why they provide the options they do.
What that means to you is that IF you get off your high horse and place the name at birth in the field explicitly named for that information, i.e. "Maiden Name", and then set the option listed above, everything you need and want is provided.
Meanwhile, for those of us whose interest is broader than just pedigrees, e.g. those who want biographical genealogy, they can select another option and see MORE DATA! Cool! How fabulous is that? You get what you want, those who want more get more! Brilliant!
But you want to deny those whose purposes are different from yours. You want to avoid using the field that by its name and by the display options is specifically designed for your needs, and abuse another field.
This is not complicated, Remi. I think you are primarily confusing minor aspects of display with the critical aspects of the database design. In particular, you seem, with no obvious basis, to be acting as if one of the fields is somehow a "primary key": if so, you don't understand: NONE of the fields are primary; the primary key is something that Geni creates and is invisible to us (except in some links).