Obama’s most facile argument Wednesday was this plea for gun control: “[I]f there’s even one life that can be saved, then we’ve got an obligation to try.” Vice President Biden said a week earlier that “if your actions result in only saving one life, they’re worth taking.”

The flaw in this reasoning is pretty obvious. Thousands of Americans will drown this year in swimming pools. You could save many of those lives by banning swimming pools. That doesn’t mean we have “an obligation to try” banning swimming pools.

We don’t outlaw pools because — however heartless this sounds — we weigh other goods against the good of preventing deaths. In the case of a pool, we weigh the costs to health, fun and liberty against the lifesaving benefits of banning pools. When talking about gun control, we could weigh lives saved by outlawing guns against the costs to recreation, liberty and self-defense. But the Obama-Biden “just one child” rule precludes any two-sided analysis.