The same group that killed thousands of Americans despite us "helping" them in the 80's is now fighting in Syria. It is not the responsibility of our government to police the Muslim world, it is to protect and provide the American people with security.
These people will still be our enemy after the Syrian war, you've already given them body armor, night vision goggles, and millions of dollars. These arms you give them will still exist after the war, and WILL be used against Americans, just as the arms from the 80's Afghanistan war were.