A few characters in The Two Towers have a bit of an isolationist bent (we're looking at you, Éomer and Treebeard). They simply don't want to become involved in the war with Sauron; sure, they can fight if they have to, but they would much rather live their lives freely and do their own thing. Sadly, Sauron's world-conquering ambitions make that freedom to choose absolutely, positively impossible. By the time we get to The Two Towers, isolation is no longer an option for any of Middle-earth's peoples—not even the hobbits, who, thanks to Bilbo, are thrust into the thick of things. While lots of people might want to stay isolated from all of these terrible world events, they generally can't. The sad fact is, there's no turning back now, for anyone in Middle-earth.
While The Lord of the Rings is arguably an anti-war series overall, The Two Towers makes a case for the importance of maintaining a military defense, and, in the case of Isengard, offense, too.
In The Two Towers, characters can only maintain their morality by being in a community with others. Just look at the oh-so-isolated Saruman and Gollum. They become immoral because they no longer have friends.