First, there are no "moderate" forces in the Syrian civil war. The Free Syrian Army is, at best, a marginal player. The major antagonists of the Assad regime are Islamic extremists, the al-Qaeda associated Nusra Front, Ahrar al-Sham, and the Islamic State. Indeed, one reason why the Turkish Army is so wary of getting involved in Syria is because it doesn't want to be allied with the groups leading the fighting. A "buffer" zone will allow those extremist groups to take refuge in a zone protected by Turkish air power.
Erdogan is fixated on overthrowing Syrian President Bashar al-Assad, arguing that a regime change in Damascus will weaken the IS. But many analysts think the exact opposite and cite the Libya experience as an example. If the Assad regime falls, the extremists, not the moderates, will fill the vacuum. A spillover of violence into Jordan and Lebanon is almost guaranteed, just as the Libya debacle has spread unrest throughout Central Africa.
The "buffer" is also directed at the Kurdish forces that have been so effective in fighting the IS, successfully defending the city of Kobani and liberating several other towns.
Bombing is only effective if it is coordinated with ground forces, and right now the only effective ground forces fighting the IS are the Kurds, the ones we just threw under a bus. Bombing by itself has never worked, as the Saudis are rapidly finding out in Yemen.
As for the Kurds, a little history.
One of Erdogan's major accomplishments as prime minister was a 2012 ceasefire with the PKK and a promise to deliver more autonomy to Turkey's 25 million Kurds. Erdogan saw the ceasefire as a way to bring the Kurds on board in his campaign to change the Turkish constitution and create a centralized and powerful presidency. With this in mind, he successfully ran for President in 2014.
But the promised reforms in governance, education and language rights -- the Kurds speak several dialects, none of them Turkish -- never came through, because the AKP also wanted to attract right-wing nationalist voters who were deeply hostile to anything that smacked of Kurdish autonomy.
Nor is the Kurdish community monolithic. Many Kurds -- most of them older, rural, and deeply religious -- supported the AKP because for them Islam trumped Kurdish nationalism.