Of course, one could easily argue that had we waited, Iraq would have been unavoidable. Some people think the same about WWII as well. The Afghanistan war could also be said to be unavoidable.
And if the standard for a war being unavoidable is an attack on one's country, then surely our war on Germany during WWI and I weren't justified since we were never attacked first in either case. By contrast, our airplanes were attacked many times by Saddam which, in and of itself, could be considered justification enough for war.