I would never have the gall to ask someone why they decided to have kids, even if I would not have done the same in their shoes. It's none of my business. My favorite is when people grill you about it, you say you'd rather not explain the reasoning behind your personal reproductive choices. They push the issue, often making gross assumptions about you —that you're selfish, you hate kids, you hate your parents, you're just a rebel without a cause.
Then you give them your reasons, they give you the same tired arguments you've heard a million times as if they are really trying to convince you to rethink or change your choice, then you defend yourself and said choice, and then, wait or it, they get the nerve to tell YOU that you have a chip on your shoulder? —Not ashamed to say it