If they oust Assad, it will only get worse. Assad knew ISIL (by any name) was waiting in the wings. He said so. He said peaceful protests leading to his ouster would only bring al Qaeda types to power. Look at Libya.
He should have done more to reform to end the protests, but that's history.
The US isn't being realistic concerning the drive to restore and then extend the Caliphate over the whole world (Sunni Caliphate). Obama's been talking utter nonsense about "moderate" Islam. He hasn't read, or is completely ignoring, the history of Islam: how the Caliphate grew in the first place via religious persecution/coercion (destroying other people's gods, etc.) and wars of aggression.
Some of this linked article might be able to be reasonably interpreted differently, but the thrust of it is definitely accurate and only the half of it at best: "The Myth: Muhammad only Waged War in Self-Defense."
After watching that, please don't be tempted to trash the Old Testament as if I'm not a Christian following the New Testament. It's Jesus's words and deeds in the Gospels that make the most sense to me of anything anywhere. He came to save you. If you reject him, that's your fault, not his. Whatever befalls you by not hearing and adhering to Jesus's message will be your doing, not his. He warned you. You won't have any excuses. Satan will have Satan's way with you exactly matching your unrepentant sins. That's the way of it whether you like it or not.