That is the stance the US took about Jews during WWII and we saw how that worked out for the world.
US military policy during WW II had nothing to do with Jews, a subject in which both the government and the people had little interest.
US war aims in Europe were achieved fully, and the benefits of our victory lasted for about 70 years, quite remarkable in the history of wars.
In WWII, the problems in Germany were metastasizing to the rest of the world. In Syria, the problems would mainly stay there. I do not think that there is a danger that Syria would start invading other countries.
There are plenty of examples of genocidal situations where we did nothing. The policies have always seemed to be that as long as a dictator remains confined in his country's borders, he can do what he wants. Or as long as bloodshed remains confined within borders, we don't really care.
Not many people got worked up over or even knew of the atrocities of Ruanda and Sierra Leone. Or Uganda. Or China's treatment of Tibet. Etc.