We tolerate quite a few mass murderers in charge of countries. We attacked that one because, supposedly, he had the tools and intent to attack the United States

We tolerate quite a few mass murderers in charge of countries. We attacked that one because, supposedly, he had the tools and intent to attack the United States with chemical weapons. Many were opposed to that war, not because they didn't feel it was right to eliminate a mass murderer, but because that was not the stayed reason. The stated reason in fact turned out to be false, and was arguably an abject lie. In other words ... it's not a great example of what you're trying to claim.