Baby Gender

I really do not understand how some get so upset by the sex of their baby! I mean come on... You knew you wanted a child, you knew it could be a boy or a girl... So why would you be so upset and resentful that you didn't 'get what you wanted'???! 
I find it absolutely ridiculous, many people have said it and its because its true... YOU SHOULD BE BLOODY GRATEFUL YOU ARE HAVING A BABY SO GET OVER IT AND KEEP IT TO YOURSELF!!!
And no... I am not bitter, I am currently 15 weeks pregnant with my first baby and FULLY appreciative of the fact that it may be a boy ir a girl. I just want a healthy baby! 😡