It is always useful to take a step back, look at some (not so old) history and place yourself within the given new context.
Pro-Assad people will never hesitate to blame pro-opposition in Syria to support IS, Al Qaeda and sometimes as far as Zionism. They will point out how evil powers of the world are all plotting to make the Assad regime fall, including Turkey. In fact, the latter is allowing Jihadis to pass by its porous frontiers and getting directly to the front.
But what about the role of Syria in the Iraqi turmoil ? Let’s quote some parts of an article in the Guardian.
Like the Americans, General Kamal was convinced that Syria was destabilizing Iraq, an assessment based on the interrogations of jihadists who had been captured by his troops. Throughout 2009, in a series of interviews, Kamal laid out his evidence, using maps that plotted the routes used by jihadists to cross the border into western Iraq, and confessions that linked their journeys to specific mid-ranking officers in Syrian military intelligence.
General Kamal was the director of intelligence of Iraq’s Interior ministry.
As Isis activity ebbed in Iraq, he had become increasingly obsessed with two meetings that had taken place in Syria early in 2009, which brought together Iraqi jihadists, Syrian officials and Ba’athists from both countries. […]
The attendees included senior Iraqi Ba’athists who had taken refuge in Damascus since their patron Saddam was ousted, Syrian military intelligence officers, and senior figures in what was then known as al-Qaida in Iraq. The Syrians had developed links to the jihadists since the earliest days of the anti-US insurgency and had used them to unsettle the Americans and their plans for Iraq.
Abu Ahmed, a “senior official” within IS adds.
“The mujahideen all came through Syria,” he said. “I worked with many of them. Those in Bucca had flown to Damascus. A very small number had made it from Turkey, or Iran. But most came to Iraq with the help of the Syrians.”
To sum it up, the Syrian regime of Al-Assad helped Jihadis install chaos in Iraq. Those Jihadis then used the chaos in Syria and grew much bigger than they intended to.
Before blaming Turkey and their evil plans, (and you have every right to do so), take a second and think about the Syrian contribution to terrorism in the region. Blame both.