I believe the question boils down to does one nation have the right to dictate to another whether they can have WMD. The aruguments about it’s OK to have WMD if you’re a democracy doesn’t seem sufficient. Keep in mind the country that is being prohibited from amassing WMD does not participate in the other country’s elections.1
Keep in mind that US is the only nation to use nuclear weapons. And they did so against civilians. This is not meant to hijack the thread, but to show that whatever Saddam might do, has already been done by the US.
As far as Saddam’s bioligical and chemical weapons, those programs were started with US’s blessings. As reported in Newsweek, he was paid a personal visit by Mr. Rumsfeld during the war with Iran. At that time, the US representative found nothing disturbing with what he was doing.
Now, in all honesty, I believe that Saddam is a menace and his neighbors and his own people would be glad to see him gone. The real problem lies with US policies that allow creation of such monsters, that later on have to be dealt with innocent people dying on both sides.