You can take that position on the Spanish-American War, but it wasn't his war. He wasn't President. He did appoint the Pacific fleet to intercept the Spanish fleet in Manila, but that was smart policy since war was declared (technically Spain declared war on the U.S. and then Congress back-dated their declaration to declare first). People in San Francisco feared the Spanish fleet and the U.S. Navy had no idea how bad the Spanish fleet in the Pacific had gotten. Then he resigned his position as Assistant Secretary of the Navy to fight in Cuba. If you want to fault him for supporting the war, fine. If you want to criticize the post-war occupation of the Philippines, sure. But he didn't create the Spanish-American War.
I think the Roosevelt Corollary was justifiable in the circumstances. Britain was going to shell Venezuela to collect debts. Out of courtesy to the U.S., they asked Roosevelt for permission. Roosevelt initially said that the U.S. would not intervene if European powers wanted to "punish" American nations for "bad behavior." This was insanely unpopular among the American people, so Roosevelt announced that the U.S. would take the "police role" in the Western Hemisphere. It essentially replaced the British in that role. Given the circumstances, it was probably justified, but the policy itself was abused, both by Roosevelt and future Presidents.
That's not a great defense, but I think his role negotiating the conclusion of the Russo-Japanese War should be looked at as generally positive. There are criticisms of it, but I'm not sure a different arbitrator would have done better.
