Not trying to be a dick, I just don't think you're as ignorant about the subject as you're claiming to be. If you are, that's fine, but I've long operated under the assumption that you're not.
2,996 people lost all of their freedom, as well as their right to live, on that day. The US Constitution is clear: its purpose, among other things, was to, "insure domestic tranquility, provide for the common defence...and secure the blessings of liberty to ourselves and our posterity." "Fighting for our freedom" may be useless sloganeering and sometimes inaccurate but I wouldn't say it's always inaccurate. Ousting the Taliban-controlled government in Afghanistan was, arguably, done for the freedom of millions of American citizens. Al Qaeda was hit hard and only recently have their quasi-affiliates regained some of the strength and power it once wielded.