If you think you're often morally obligated to suppress the favoritism you naturally feel for your children, why aren't you morally obligated to suppress the far milder favoritism you naturally feel for your fellow citizens?
This, by the way, is why I emphasize the notion of the half-full (and thus also half-empty) glass so often. If "you're often morally obligated to suppress the favoritism you naturally feel," you're often not morally obligated to suppress the favoritism you feel. Thus, for example, it's not morally right for America to invade Canada,  but it's also not morally wrong for America to keep Mexicans from invading America.
This idea that the glass tends to be part-full and part-empty at the same time isn't some novel insight of mine. Aristotle, for instance, liked to point out that life is full of trade-offs, perfection is unlikely, and the best you can do is some kind of optimum. (Confucius  said something like this, too.)
But, I'm a notorious extremist, always going around citing Aristotle, Benjamin Franklin, the Preamble of the Constitution, George Washington's Farewell Address, and other fringe crackpots.
Last week, Bryan got rather badly schooled in his comments section. Now, he's back with three more posts