I agree that we have a problem with population growth and that our perceived liberties(no children/etc.) are threatening our future.
But: “By using the term ‘Illegitimacy’, you call the relationship of many people, including the parents that gave birth to me and by extent my very existence itself illegitimate, just because they did not follow a ritual of a set of religions practiced by a limited subset of all people in existence. Therefore, you depress me, as I do not think of your existence as illegitimate. I will not insult you over it, but I want you to see what kind of person you chose to be with your choice of words and beliefs.”