After Japan's unjustified attack on Pearl Harbor in Hawaii, America needed to send a strong message to Japan. The Doolittle Raid showed that the Japanese could not defend their emperor in their own territory. It demonstrated that Japan would not win the war in the end, and it boosted American morale.
Japan attacked Peal Harbor, a declaration of war. Clearly the Doolittle raid was necessary to diminish Japanese morale and show the Japanese leadership that they are not as secure as they might believe. The Doolittle raid was a minor bombing of Tokyo so it was not really a crime. Kk