So I realized today that the main message of the Horton movie, at least for me, was the freedom of speech and the right to think freely. The movie was about 2 of the basic human rights.
We see the first warnings from Kangaroo to discourage Horton to talk and think about the little people living in the Speck. Then hiring the "secret police" vulture going after him. Another interesting point - Kangaroo doesn`t want to get her hands dirty, but outsider vulture can do it. The conflict ends up in a witch-hunt with a public trial with crowd of easily manipulated Monkies who only care about the basic life - have kids and enough food.
Ironically, exactly the same problem is in the "Speck" world. The city council stands against any suggestions that there is a Voice warning them of apocalypse of their little world. This seems a little like 1950`s Communists - "The jungle" and McCarthyism in United States - "Whoville City" :)
In the end both worlds connect by the loud noise from the Speck and the dark spells of mind blankets are broken.
This was one of the most original story (yet adapted from Dr.Seuss' book) made by Blue Sky Studios. I`m glad someone was able to transform these ideas into the new 3d animation media that kids watch today.