They don't have to. They'll just quietly disrupt any outside support for the protesters and turn a blind eye to the murders, Syria bringing in thugs from Iran, those thugs beating up the U.S. Ambassador, etc. Syria is not a major player in oil, thus the EU is imposing an embargo. Notice in Libya it was the other way around. Gaddafi threatened to turn off the spigot and the bombs started raining thick and fast.