That's just more gibberish. It's the best possible universe because God is perfect, that tells me absolutely nothing about why a universe with one more fly is more perfect than a universe with one less. Because isn't an answer.
This is a perfect illustration of why belief in the Christian God is irrational. People believe all manner of irrational things, just look around you, and yet God is basing the judgment of their eternal souls on their ability to make a rational decision about His existence, and the veracity of some legends about His supposed Son. That's just crazy. People can't be expected to make a rational choice, because people aren't rational.
Your God ain't perfect...He's nuts.