Hitler

Can you give a reason?

The reasoning is to joke.
The answer sounds right to the listener and therefore that is what should be answered.

In practice he would do nothing for him and instead would write posts about free choice and posts about slippery slope arguments.

I assume the reasoning is clear. If you want to ask something, please ask it yourself and don't ask me to formulate the question and answer. If you are hesitating between reasonings, please present them.

The hesitation is because this is a baby who has not sinned and is not currently persecuting. Those who hold to free will believe that this is not included in the current definition of the situation either - that in the future he will kill. The fact that we know that in the future he will sin does not permit killing him, and as Chazal said about Ishmael, "where he is there."
(And indeed, there it is about what his sons will do after several generations, and it would be possible to imagine, on the other hand, a rebellious and mischievous son who was killed for his own sake. But a rebellious and mischievous son is killed in the legal definition for having disobeyed his father and mother, and what Chazal said about being killed for his own sake is like a kind of taema dekra.)

Or do you mean that in the face of a catastrophe on such a historic scale, all rules are null and void and everything must be done to prevent it (even something that is a complete injustice, since according to the definition of the current situation, you are killing an innocent baby), and just as they used to kill innocent civilians in wars.

These are just word games. The questioner's assumption is that I have certain information, meaning there is no possibility that he would choose not to do so. If there is no certainty, then clearly he should not be killed.