US wanted to remove Assad - whatever we think of Assad US does not have the right to go into another country and overthrow it's leader - as it has several times in the past
France wants to remove Asad. USA is very wary (they remember the bad experience of Iraq and the removing of Saddam). The problem with USA is that Obama hesitated all the time to intervene and when he did it, it was too late : against ISIS, against Asad.
Now Asad can not stay as the leader of Syria, because Syria is finished. He might stay as the leader of a tiny Alawiland but Alawi people are probably fed up with him also. They support him only to not become in the hands of Sunnis. For that reason Syrian Christians support him also in Arab regions (Kurdish areas are different).
Sunnis will never accept Asad anymore and now there is only a Sunniland torn between ISIS, Al Qaeda, Muslim Brothers and many foreign Jihadists who don't care about Syria.
Kurds are torn between pro-Öcalanistan and the rest of a Kurdish population who don't support Öcalan (many of them hate PKK) but don't want to fell in ISIS hands.
In that battlefield the obstination of Asad to bomb Aleppo is criminal, because Aleppo is lost for him.