genetic programming does prove that you cannot simply assert something is impossible due to improbabiliy. You don't need genetic programming to tell you that. All you need enough common sense to notice that "improbable" does not mean the same thing as "impossible". Fairytales may be improbable, but not necessarily impossible.
In this case, "impossible" simply means having such a low probability that it won't happen in a specified period of time. IDers claim to have calculated the probability of certain things happening. The success of this programming method proves that useful and previously unknown things can arise through mutation and selection.
That does not "prove" it happens in biology, but it demonstrates the weakness of the "improbability" argument.