The French and the antiwar apologists such as wbwolf argue that inspections should be allowed to run their course, claiming they are working. The only reason they're working at all is that Saddam is using them to delay the war; by backing this argument, the French are helping him stay in power. If we back off now, we'll discover that the inspections have quit working - and, in the meantime, Saddam will have succeeded in his objective to delay the war into the summer. This would cause even more casualties than fighting now will.
Yes, we risk an environmental disaster, as well as casualties among innocent Iraqis (though I question whether there are any such; by not rising up and throwing Saddam out, it can be argued they brought it on themselves). The blame for those can be laid squarely at Saddam's feet. If he'd disarmed, as he agreed to in 1991, none of this would be necessary. We cannot let more of his potential crimes against his own people and the environment to dissuade us from doing what must be done. If we do, he wins.
As for following the rule of international law, it's broken down. Any law must back up its pronouncements with effective means of enforcement. There are no such means here, as the UN has plainly refused to put teeth into its 17 resolutions on the subject.
I'd have posted this to wbwolf's LJ as a comment, but he's too busy preaching to the choir to hear dissent.