The transfer of aid be it military, training, economic relief, or humanitarian aid to the organizations that make up the vast majority of the "Free Syrian Army" is a threat to homeland security. The "Free Syrian Army" is composed of terrorist organization that have attacked American targets as well as our allies. They have carried out suicide attacks and are actively engaged in the destruction of non military targets in Syria I.E Shi'ite religious buildings and books.
By aiding these groups, America is providing aid for future terror attacks on any group. The tax payers of America do not support the arming of "rebels, terrorists or non recognized government armies, mobs, militias or freedom fighters."