True, you can't declare war against terrorism in the proper sense. However, I think that in the practical sense, 9/11 certainly rose to the level of an open act of war.
I absolutely feel where you're coming from, I mean, I too felt as if they should be tried as war criminals, they were being detained and questioned just like POW's, so why not?
But this is an emotional reaction. It just so happens that Congress granted Bush the power to hold them as if they were POWs, even though they technically weren't (and as we can see there was FAR too much leeway in that decision). Bad move by Congress, one of many (Patriot Act = serious infringement on negative rights (and no, I'm not a Libertarian)).
The difficulty is a Law is absolute, and can only be changed by amendment or referendum. You can't justify side-stepping it based on things like "9/11 was SO horrific" ... I won't even go into how 9/11 equates to the dozens of similar strikes -by us- in other countries (which is what these militant groups feed off of for their propaganda.)
And so as such, because we are a nation of laws, and we live by our laws, and as a member of the international community are bound by our laws, we cannot simply throw the rule book out the window whenever it suits us. 9/11 was no more a Military Strike than when the "Irish Republican ARMY" sets off a car bomb in London. Way more deaths, sure. More destruction, sure. But irrelevant are those numbers. They're peas of the same pod. Terrorist actions, the same such actions that any human can do with the right determination and training.
A proper act of War, may have many more casualties, or far fewer, but it's so distinguished because it's carried out by a nation's military. al Qaeda is an army with no nation (like the IRA***) and cannot technically declare war, or have war declared on it, regardless of how devastating their actions.
So, in practical terms even, no it wasn't an act of war. It was just a heinous act.
There are legitimate reasons to support federal trials or military commissions, and I think people can and should question the way that the war on terror has been prosecuted. But I do firmly believe that this is a war, declared or not, and that the military tribunal system offers advantages to dealing with enemy soldiers. They may not have a nation, but I don't think that really affects the practical nature of this conflict.
The advantages a military tribunal would grant are null on civilians. Terrorists are civilians with explosives and bad tempers. If we don't treat them as criminals, and instead treat them as war criminals, then we vindicate them; we are elevating their status by doing this, also we subject ourselves to a much unwanted cross-reference by other nations, just more examples of how the US doesn't practice what it preaches.
Health Care ... strike. (so far)
9/11 Trials ... strike. (too bad too...)
Unemployment ... strike. (not discussed much here, but most of his 'accomplishment' is in the public sector)
I know this isn't baseball, but ... yeah. It's not looking so hot. I mean if I'm even thinking we made a mistake in him, I wasn't just swept up in the fervor to vote for a black man, but I'll admit I wanted him because I didn't want the McCain/Palin ticket.
And this brings us to why we need election reform... but that's another thread.
*** Just to clarify, the IRA is based in Ireland, yes, but its members span dozens of nations, which is why it doesn't fit under the belt of an actual Army, they're just called an Army and Irish happens to be in the title too.