Wretchard, that does ring true to me from an economic standpoint but I was also thinking in terms of culture.

Say you’re a native of some EU country, the Netherlands for instance, that is undergoing demographic collapse/displacement. You’re aware that at this point, only a massive and sustained baby boom among the native Dutch will be enough to reverse this collapse, and you and your spouse want to do your part. Your problem is that you can only control your own “output”, not anyone else’s. In other words, you could have ten kids and raise them all to be good Dutch folk, but unless a critical mass of your fellow Dutch do likewise, again something you have no control over, the demographic collapse will continue unhindered by your family’s gallant but ultimately puny efforts. To make matters worse, when the collapse finally comes to a head and drags your country into the abyss, those ten kids are just going to be dragged down with it – assuming they (and you) haven’t long since fled Europe for other, friendlier shores by then. Either way, your original purpose for bringing them into the world in the first place has been defeated.

We may be able to avoid an economic “tragedy of the commons” as you suggested, but I’m not sure there is an equivalent demographic or cultural remedy, short of actually going to a clan/tribe system. And even that might not work if the clan/tribe system proves no more resistant than nation-states are now to the corrosive effects of the emerging “global cafeteria culture” I mentioned in a previous post.