the flip side of the coin

I read somewhere--I believe in Sophie's World by Josten Gaardner--a description of the dialectical constitution of good and evil being like a coin with good on one side and evil on the other. The larger one side of the coin becomes, the larger the other. And thus we can only know great good if we know great evil. The policy implications may be staggering. All we need to do is to find an evil that causes less disutility than the corresponding good. "So," as I said to my college roommate on the phone, "Do we kill more babies to increase the good?" Killing babies, in retrospect, is probably not the best evil to use. In fact, it is not clear from that it is possible at all to increase net utility if we accept this framework--or perhaps, I should say, utility must be equal (and therefore, "maximum," though in the case of equality it becomes trivial) no matter what the size of the coin--if, that is, we define good as what increases utility and evil (or bad, if you'd prefer) as what decreases it.

Of course, like all similes, the good/evil coin may be totally misleading.