Syria doesn't have the oil resources, military might or the weapons to be a threat to the United States. Syria's civil war is an internal struggle and a regional problem. Unless the war spills into Turkey, Jordan and/or Israel, the United States needn't worry about the Syrian regime and their small stash of chemical weapons.
The US has a historically demonstrable habit of inserting itself into the domestic and international affairs of other countries under the guise of humanitarianism. We see after the fact that many of these interventions were thinly veiled attempts to protect their capitalist interests, though the US public usually remains oblivious to these motives at large. US citizens are then surprised when these countries harbor ill-will and threaten violence. The best way to avoid military reprisal is to avoid armed defense of our economic interests.