If you think that simply having children makes one selfless, I recommend talking to like... 80% of the people with parents for five minutes about their childhoods.
Blood-and-soil types get a little antsy when you suggest letting in... people with perhaps a more tan complexion, let's say. They tend to dress it up with other language, though.
No, there's an _economic_ threat to declining births (and also a demographic threat makes certain classes of people... well, let's just say "itchy"), but that is an entirely artificial problem that we could solve, if it wouldn't hit NBC Universal on the pocketbook.
There's a weird vaguely-evangelical bent here that is, ultimately, not surprising, but still jarring. Threads about having children tend to bring judgemental parents out of the woodwork to tut-tut anyone who dares to choose a different path.
I knew it wouldn't be long before the blood-and-soil folks came out lol. Why do you feel the need to suggest not becoming a parent to someone who just said it wasn't the life they wanted? Do you mete out the same judgement on parents who also should have abstained?