Although, it is terrible what the civilians face in Syria we need to stay out of the conflict. Military strikes and/or arming the rebels signifies our lack or respect for other countries who believe it is none of our business. It is not our place to take sides in their civil conflict. The rebels can surrender and come to an agreement.
Assad should not be bombing his big cities full of civilians but if the entire world will not act then we should take the stance of agreement. The world (including close allies of Syrian government), is against military action so we should be with them on their decision.
ALSO, ARMING REBELS WILL ONLY INCREASE AND PROLONG VIOLENCE.
We do not need to make enemies with the world. Involvement will not make America hero's; it will only make us seem hostile.