It's also a function of religions. Catholicism among other religions inveighs against birth control, even natural rythm. So, a Catholic who tries to follow church teaching must eschew intercourse or use birth control of some sort and risk mortal sin. Still, the unmitigated conception and birth of children beyond one's means to support and care for them is irresponsible. Of course, people who have kids like it's going out of style probably never stop to think that they might drop dead and leave the raising of the children to the surviving parent or society.