A Serious Strategic Question for the Iran Factor Proponents

Some strategists weighing in on military action in Syria cite Iran and the importance of Syria as a buffer between Iranian domination.  They list the importance of a US-friendly regime in Syria as a vital US national interest.  Yesterday on Fox News, General Jack Keane explained this view in-depth.  Certainly a containment of Iranian domination in the region is a vital national security interest, so don’t take this question the wrong way.  My question is what factors indicate that a US-friendly regime in Syria is remotely likely, even if we do assist in toppling Assad?  Our Iraqi experience? Our Afghan experience?  Our more recent forays in Egypt and Libya?  On what basis do General Keane and others, who toss out this pipe-dream as a likely outcome,  base their strategic reasoning?  I would love to hear the historical backing for this position!  Sure, lots of things would be advantageous to the US, but we need to take off the rose-colored glasses and look at the Arab/Muslim world as it is and it is anything but friendly toward US national interests.  We need to deal in reality here – not wishful thinking again!!!