Recently, Spain sentanced terrorists convicted of, well, terrorism for the Madrid bombings. No "enemy combatant" status, no "prisons held off of the shore", no suspension of habeas corpus. Just good old fashioned trial like it was any other.
This response rather reminds me of when the Philippians prosecuted their terrorists a few years ago.
Using the court system brings the issues to light. It tells people - openly, without fear or prejudice, "This is how these criminals work". Now, all people can see what to avoid.
It brings the arguments and plans of these groups into the open, rather than keeping them in the shadows. Instead of mysterious, unknown reasons other than "They hate our freedoms", their grievances are now part of the public record, and shown where they are faulty in the eyes of the law and the community at large.
This prevents would-be terrorists from recruiting others based on ignorance. It's no longer "The evil infidels/imperials/etc are keeping us down because they hate us" - they lost that argument when the full use of an open court system is used. Then, they are shown that they are "kept down" because they conspire to kill innocent people for their own selfish reasons of power.
It also keeps the government in check - if the government is itself performing actions that are not in keeping with an open and just society, then it will be forced to expose this as well, which means that people can make positive changes *without* resorting to violence and terror.
And finally, the open court system has the same result as "secret renditions and using enemy combatant" techniques does - it puts terrorists and their supporters in jail, or in the execution chamber should the laws of that society demand it. Not in secret, not by violating people's civil rights, but by *using* those rights and legal powers - even on those we would despise the most.
That is what using an open court system does when applied to terrorists. And why the United States should be doing the same.