So, you're assuming that, while WE have nukes, we're RESPONSIBLE enough to be entrusted with them, while if our enemy nations had them, they would even ignore the inevitable prospect of MAD in their haste to push the button? Come now. Saddam may be a psycho and a despot, but his actions show he's no idiot. He's at least as safe with a nuke as we are.
However, were there any evidence that he HAD nukes and WAS preparing to blow us into the stratosphere (Just who, I wonder? We're an extremely large nation. He could aim for DC, I suppose, and were he really, really advanced the shockwave would just about reach the Pentagon), invasion would be justified.