ID's do not mean much in regards to security IMO. Some Pacific Island countries sell or sold passports in the past. Plus, and here's the kicker, many of these Pacific Islands residents are classified as full residents of the USA and are not required to have a VISA or GreenCard or anything to enter, live, get benefits etc... They used to enter with an island drivers license or a copy of the Island Birth Certificate up until two years ago. Many people can obtain documents abroad and enter the USA, plus IMO any organization that has decent capacities to create some chaos should be able to obtain fake documents anyways.
But.... and here's where I'll probably get flamed on, what's wrong with proving citizenship to get a DL or other documents / benefits??? I thought the ACLU was concerned with "American's" Civil Liberties, and not the Illegal Immigrants Civil Liberties. What is wrong with requiring people to have either legal entry into the USA or be a citizen to have a DL? I see nothing wrong with tightening up laws regarding Illegal entry into the USA. If the policy makers need to use 9/11 as a way to push these laws then it is a sad state in American Politics that we are more worried about offending and protecting Illegal's then we are about Legal Citizens.
I look at this from a different view, try living overseas, many of the countries take millions of your and my tax dollars each year and bad mouth / hate the USA. The residency requirements and paperwork and rules and regulations for American's to live overseas is not always simple depending on the country. To travel, sure a US Passport is a wonderful thing, but that is travel, many countries want the american tourist money and then for the American's to get out. Having gone through a lot of difficult times overseas I have no problem with laws that make it difficult for ILLEGALS inside the USA no matter how the lawmakers have to create them.