There was a lot less protest for that war for some very particular reasons (okay, so this is still world politics...oh well).
One, the war was against Al-Qaida/the Taliban/Osama Bin Laden and not Afghanistan, that just happened to be the country they were (primarily) located in.
Two, Al-Qaida (is it with an "i" or an "e"? I've seen it both ways) made an EXTREMELY aggressive first move - they hijacked commercial airlines filled with completely innocent people and high-speed crashed them into building filled similarly innocent people. About 3,000 people died in one day; heck, within two hours! And not just Americans, people of all nationalities and origins were victims of that attack. I don't think I need to argue how, well, evil the attacks of 9-11 were to anyone.
Bin Laden's group made a clear first attack and declaration in doing that. Not many people were going to argue with bringing down his organization and him. We hadn't sought him out and attacked, he was the one doing that.
Now, Iraq on the other hand, while not having a shimmering white & pure past, has recently not really done anything antagonistic or aggressive. In my opinion, yes, they should be held to the UN weapons regulations if they are a part of the UN in any way. And they've been a problem in the past, so yes, some caution and careful watching should take affect as well. But declaring war pre-emptively? There's no reason for it. Especially when so many other countries are against it, and Iraq does seem to making concessions now, trying to take steps to avoid a war. Of course, one can argue they are only doing it because we threatened to start a war with them, but they have still shown signs of "backing down" so to speak.
It makes sense that more people are protesting this war because we (America) are the ones being the agressors, finding reasons and excuses, and basically war-mongering. I'm very anti-violence...I hate it, and war will never beget peace, it will onyl beget more war because people's memories are often too long, and their pride is too easily wounded.
On a down note, I heard on the radio this morning that a lot of those "human sheilds" left because it was getting too dangerous. !?!?!? Well, duh!!:-/