I have similar thoughts, though perhaps not for exactly the same reasons. It seems to me that in discussions that touch on population ethics, a lot of people seem to assume that more people is inherently better, subject to some quality-of-life considerations. It's not obvious to me why this should be so. I can see that if you adopt a certain simple form of utilitarianism where each person's life is assigned a utility and then total utility is the sum of all these, then it will always increase total utility to create more positive-utility lives. But I don't think my moral utility function is constructed this way. Large populations have many benefits--economies of scale, survivability, etc.--but I don't assign value to them beyond and independent of those benefits.