That's needlessly reductive. Chemical weapons are banned, but Saddam didn't use them against US troops in the US invasion. Bans are probabilistic, not binary.

That's needlessly reductive. Chemical weapons are banned, but Saddam didn't use them against US troops in the US invasion. Bans are probabilistic, not binary. Anyone violating a ban must weigh the advantage from doing so against the consequences and probability of getting caught. A high degree of revulsion and a consistent track record of enforcement greatly increase consequences and probabilities, and make a ban more effective. Just shrugging your shoulders and saying it's not always possible is a sure way to increase the probability of unwanted action.