It takes two to tango. Assad is killing revolutionaries, and revolutionaries are killing government troops and supporters. And both sides are killing noncombatants who happen to get in the way.
There are terrorists on both sides. But, bad as Assad is, the opposition is even worse.
Assad must step down to end the fighting? How about if the revolutionaries stepped down and ended the fighting, instead?
No, it doesn’t take two to tango. It takes Assad being advised and encouraged by his Russian and Iranian allies not to deal with the original protesters and try to implement some reforms. Now it’s a mess, and it’s entirely the fault of Assad and his allies.