Michael Anton: "Why Do We Need More People In This Country, Anyway?"

We don't.
Anton's absolutely right. In fact, in my opinion, we kind of need fewer. We ought to be thinking in terms of incentives to help us work toward a somewhat smaller population. (And it's easier and better to control immigration than to try to influence domestic birth rates.)
   But: that's just one kind of consideration. I'm not in favor of micromanaging such things. And there are important considerations other than practical/consequentialist ones. In general, and within reason, more free movement is better than less free movement; it matters that some people just want to come here. In the absence of good reasons to say no, we should generally say yes. Furthermore, we have an obligation to help those genuinely fleeing violence and oppression--again, within reason. But things have gotten bad enough that we now have to start seriously considering the adverse environmental and social effects of a rapidly-increasing population and masses of unassimilated, often illegal, immigrants. (Incidentally, I also tend to be in favor of more foreign aid to countries south of our border; they need it, and it would help solve our illegal immigration problem.)

   Anyway, we should not be mindlessly pumping up the population, we should re-think our policies and honestly ask whether a brief hiatus from mass immigration--and a major re-evaluation--might be good. Currently, both sides want to inflate the population, and no one will honestly consider the effects. Many on the left have a thinly-concealed open-borders position, and even oppose any effort to stem the flood of illegals. They think that any attempt to reduce or even control immigration is racist (though, of course, they think that everything is racist...). On the right, many libertarians are pretty up-front about open borders. Many conservatives want an ever-growing population as a means to an ever-growing economy.
   So both sides are supporting a policy that could be disastrous. The population can't grow forever. And, with the vanguard of the left preaching racial tribalism and an anti-assimilation gospel...well...we just don't know how many people are listening. This might all work out fine. Or it might be a catastrophe. We need to be putting a lot of resources into asking how likely the latter is. Of course this is one of those questions about which many people just can't be honest--they're devoted to a conclusion, and they can't/won't actually question it. All they do is hunt for rhetorical pseudo-reasons to support what they already think. But that's not unique to this question. We at least have to try to be a little more rational about it.