Why did Gandalf save Faramir?

[Eomer of the Rohirrim]

To be a, no doubt very basic, Devil's advocate, isn't there conflict between means and ends here? Great atrocities have been carried out in the pursuit of a higher purpose. Or is it just that Eru decides what is moral and what is not?

Maybe then Gandalf's decision was not a moral one, but there's the added bonus in the story of the author postulating a god. In non-fiction at least it's a classic moral dilemma, but it could lose something in adaptation.