How can a child be illegitimate?

I used to see a lot of Hindi movies and even today I do that once in a while. Illegitimate child as an expression is very widely used in the film industry and perhaps the ground realities are also no different. Every child is created, nurtured in its mother's womb where it remains safe and protected before it is time to come out. No child has the flexibility of choosing its parents as decreed by the nature. It comes into the world without exercising any choice. So how can some be labelled illegitimate when they don't even know its meaning? As such legitimacy of a child is a purely social norm and has nothing to do with the natural phenomenon that doesn't differentiate between a legitimate child and a illegitimate child. Can a social norm take precedence over a natural phenomenon especially when the child concerned hasn't exercised any choice in the matter. Even if there is something wrong or some differentiation is necessary the parents should be held accountable. The current practice is perhaps a reflection of the fact that the rich and powerful can pass on the blame to the less fortunate or vulnerable people and get away with almost anything. The society as a whole seems to support them rather than the poor and the helpless. Else how can a child become labelled as illegitimate even before it is born? So instead of saying an illegitimate child perhaps it is time we said child of illegitimate parents. If someone has to take responsibility, let it be the one who is aware and who exercises his/her choice in the matter. Incidentally Leonardo da Vinci who is considered to be the most most diversely talented person was illegtimate.