Perfection: our younger son, a philosophy major, insists there is no such thing. I disagree, because nature provided kittens.     True, kittens don’t stay kittens for as long as I’d like. Our house is too small to continually add more. So until we can retire to a cat ranch, my husband and I enjoy perpetual kittens as part of a five-county foster-home network. The payoff is twofold: along with contributing to an orphan’s bright future, we get the playtime fun a...