Listen to Gary Sick (also: wikipedia)
‘…Saudi Arabia’s decision to place the political threat from Iran above the actual military and ideological threat from radical Sunni Islamism is questionable at best. Both Al Qaeda and the self-styled Caliph of the Islamic State have openly proclaimed their intent to overthrow the corrupt Saudi royal family and take control of the two holy places—Mecca and Medina—that define the Islamic credentials of Saudi rule. Indeed only last week ISIL claimed responsibility for the bombing of a Shiite mosque in eastern Saudi Arabia that killed more than 20 people.
This threat from radical Sunni Islamism is the only credible external threat to Saudi independence and territorial integrity. No other movement, state or institution in the Middle East has undertaken anything remotely like this concerted anti-Saudi campaign. The Iranian regime has never evinced an aspiration to destabilize, much less attack, Saudi Arabia or any other Sunni state. Iran’s horrific eight-year war with Iraq in the 1980s came in response to an outright invasion by Saddam Hussein, explicitly supported and funded by Saudi Arabia and the Gulf monarchies.
Today, Saudi Arabia, together with Qatar and Turkey, is supporting and funding radical Sunni Islamists in Syria (Nusra Front and other al-Qaeda affiliates). This effort may well achieve its goal of overthrowing the Assad regime, or at least carve out a mini Sunni state within Syria, but the result would be to empower a vicious and uncontrollable coalition of extremists whose policies make them essentially indistinguishable from ISIL. Deposing Assad will not end the Syrian civil war; it will simply reverse the players, turning many current regime supporters into insurgents while fueling a contest for supremacy among the Al-Qaeda militias and ISIL….’
Via Saudi Arabia's Widening War – Gary Sick – POLITICO Magazine
Part One and Part Two.