You could say it's not about winning. Assad will take control of Ghouta, that's certain. But Assad has little actual popularity, even amongst his own supporters. He will never win the people over so he has to make them fear him and never do anything like rebel against him again. This is the tyrants way.
Last time he done something like this, the massive dump the "international community" took was to give him advance warning to remove his men from the airbase, then some superficial damage that looked good for the camera but was easily repaired in a few weeks.
If that's the fallout he will expect from an international community that has already isolated him, then I wouldn't be surprised if his advisors have calculated it being a small price worth paying to brutalising the remaining pockets of resistance and to give out a clear warning to anyone who dare oppose his rule.