If the Islamist rebels win in Syria, one of the first things that they will do is slaughter the Christians. Yet our government supports the Islamists and opposes the Christians.
Russia does the same thing- supporting Shia islamists of Hezbollah and the IRGC. For Russia their interests are and always have been a seaport directly on the Med... and whatever secures that is their goal. Iran’s interests are to use Syria as a means of confounding Israel and projecting their power and influence into the nations all around the Med, too.
The Islamists whether Sunni or Shia, are mere puppets providing plausible deniability for their masters, and are secondary to the political, defensive security needs, and offensive ambitions of all the nations involved.