Infield fly rule doesn't come into effect with a single runner on. There has to be two or three runners on and less than two out. With a single runner on, there's no real potential to trade one out for a chance at two by letting a popup fall, only to trade an out on the batter with an out instead on the runner at fisrt. This occasionally happens, when there's a notable difference in baserunning speed, and the infielder is able to think fast, and it's perfectly legal. Runners first on second getting consecutively forced at third and second after letting the ball drop would be a far less-than-automatic play, I think. But even if it's routine, it's action. Balls drop in often enough as it is.