As far as their comment in particular:
> So don't have kids, we're not running out of people after all.
This adds zero to the conversation. It's like saying "You might get hit by a bus if you try to cross the street, so don't do it at all".
In truth, deciding whether to have kids is a much more complicated process than that. There's no "So just do X" or "So don't do X" advice that is helpful or constructive.
Much of human sexual morality is rooted in the thorny issue that mother nature makes sex pleasurable in large part to get you to reproduce and efforts to enjoy sex without it leading to babies are often unsuccessful. So, we have a long human tradition of things like shotgun weddings.
Yes, by completely changing your plan for your life you can prevent certain problems, but that doesn't necessitate that you should make the change.
I've wondered whether we might be seeing a new division of labor emerging: An increasing number of educated professionals elect to have few or none of the kids needed for the next generation of workers, while some lower-income people take up the slack by having lots of kids. This might actually be a sustainable social model, but it would require two things: (1) "Talent," however you choose to define that, needs to appear in sufficient numbers of children born to low-income parents and not just in children born to educated professionals --- my guess is that this is indeed the case; (2) crucially, society must be able to provide the infrastructure needed to raise children to productive citizenship, especially when some of these children are being raised by parents who don't personally have access to the necessary financial- and other resources --- and that's very much only a partially-solved problem.
