Hypothesis: To defend that it is sometimes moral to lie commits us to the Nietzschean death of God.
Sloppy argument with most of the relevant ideas:
The death of God, so far as it has a theoretical and not merely factual basis, rests on the idea that the will to truth is simply another manifestation of will to power since it can claim no objective basis.
The will to truth is seen to have no objective basis when we see that life demands that it is sometimes better to deceive or be deceived.
But to defend that it is sometimes moral to lie is to claim that it is sometimes better to deceive or be deceived.
Put another way: as soon as we claim that truth is a contingent good, it loses its power to be a governing ideal. When we ask “is truth good?” we have to look to something other than the truth to answer the question, e.g. the “right to know truth” or the wild and not entirely logical character of life.
I don’t intend this argument as a condemnation of right to lie arguments – if you defend such arguments, it can be taken as a way to lend support or find some sympathy with Nietzsche. That said, it does seem to increase the cost of defending the right to deceive.
Nietzsche is, for me at least, at his most sympathetic when he tries to articulate just this sense where life is simply too complicated for ideals or absolute values. But once we start down this path, we lose any value transcending absolute flux: God, moral absolutes, scientific law, etc, all of which are attempts to carve some transcendent order out of the supposed wild flux of life. And no, openness to falsifiability in science does not get past this.