The United States has drawn stark lines between acceptable and unacceptable kinds of warfare -- and created a double standard in the process.
The United States announced that the use of chemical weapons by the Syrian government would be a "red line," potentially triggering intervention. The White House fears that "an increasingly beleaguered regime" may be plotting a chemical attack. Secretary of State Hillary Clinton added: "We are certainly planning to take action if that eventuality were to occur." Oddly, the international community seems less concerned by how many people the Syrian regime kills than by the methods it uses to kill them.
The rule of murdering your population is: Don't use chemical weapons. We often draw a sharp distinction between "civilized" conventional arms and intolerable weapons of mass destruction--or the evil triad of chemical, biological, and nuclear weapons.
Blowing your people up with high explosives is allowable, as is shooting them, or torturing them. But woe betide the Syrian regime if it even thinks about using chemical weapons!
A woman and her child under fire in Aleppo might miss this distinction. It's not obvious that high explosives are inherently less evil than chemical weapons. People vividly recall the horrifying gassing of soldiers in the trenches of World War I. But it was artillery shelling that killed in hugely greater numbers.