I disagree.
Starting a war with another nation can justify terrorist attacks in the eyes of some. You're leaving a generation of children who feel as though they have a legitimate grudge with the USA.
Say, hypothetically, that Germany was attacked pre-emptively in 1939. German people of the next generation would be more inclined to dislike American/British people if they thougt that they were unfairly targeted, which would lead to long-term European unstability. As it is, it's a lot harder for Germans to say they were unfairly treated during the war.
Also, I disagree with you saying "those people". Terrorists can come from every nation, America included. By your logic, Britain should go to war with Ireland.