I didn't have an answer, other than that I don't know how complicated the delivery system is for a chemical "suicide" attack, so it may be too complicated for individual terrorists to pull off. Any suggestions for a more substantial rebuttal for his question?
The '93 World Trade Center bombing included the use of a poison (I don't recall what) that was burned up in the primary explosion. The point is that terrorists will use whatever technology is available to them to cause havoc.
There is anecdotal evidence that some of the 9/11 perps may have been exposed to anthrax. At least one doctor who treated a 9/11 perp reported symptoms that are consistent with anthrax. The perp of the anthrax letters has not been identified.
Just because an organization hasn't used a tool doesn't mean it is not interested in it. The bomb vests can be quite effective, with the side benefit that the person pulling the trigger does not suffer. Suicide nerve gas attacks would be unpleasant for the person pulling the trigger, and therefore it may be harder to recruit subjects for such missions, even if the mission could be carried out from a technical point.
The Sarin gas attack in Tokyo is the most successful such attack so far. IIRC, the Korean guy who lit and threw a gasoline-filled liter bottle in the Seoul subway caused more death and destruction than occurred in the Tokyo sarin attack. Terrorists can "do the math" too.
Maybe Saddam was selling chemical and/or bio and/or nuclear materials to terrorists. We (the public) don't have any hard evidence of that. Heck, at this point we don't have hard evidence that Saddam had 'em, although I am confident that evidence will be forthcoming.
But the general persuasive argument is that the hazards related to chemical, bio, and radiation (not fission chain reaction/explosion) are a fraction of the hype. High explosive fragmentary devices and fire are more destructive in close quarters, than are chemical agents.
WMD: You need a high expertise just to handle these so it doesn't backfire. It's possible that the Iraqi necessary high tech guys never arrived and the WMD never got out of storage.
The second thing is that we advertised the heck out of "moonless night" but went at the full moon. I think Saddam was two weeks behind schedule.
Tell your friend to read up on Hitler and his crimes. Saddam is guilty of the same. No one stopped Hitler early on and the good guys paid dearly.