This seems to be the key talking point for Russian trolls. Assad used chemical weapons because he believed he could: there have been no consequences before for his use of these weapons. Moreover, chemical weapons are used to create terror and fear among your enemies. Assad has been emboldened by the recent military turn of events in Syria and is now looking for total victory. Consequently, the regime has been signing mini "peace" deals to move those who don't support his regime to Idlib province where he then kills them. The use of gas is meant to demoralize and terrify those who don't support the regime with the intent of either killing them or causing them to flee Syria.