There's two separate issues here:
Who's responsible for the violence and
What if anything can/should we do about it
In the first case of course all the violence isn't coming just from the government - there is now a conflict going on, partly sectarian, partly purely political. But the government controls the main armed forces and also controls the Shabiha militia responsible for frightful blood-letting throughout the country. These people take it out on any innocent civilians who happen not to have fled before they arrive to mop up after the government's heavy artillery has "softened them up".
Secondly, it seems wrong, particularly in the light of very recent atrocities, to continue to give to the Syrian regime that they can continue to behave in this way. Safe havens near the Turkish border, say, for civilians, very severe sanctions against Syrian officials at home and abroad, and overwhelming pressure on Russia to cease propping up the child killers (a difficult task the latter one as they don't appear to have any moral compass whatever), even some sort of operation such as a drone-directed operation to prevent or deter the heavy shelling. Because at the moment the Syrian government feels as though it can do as it pleases.
Plainly however arming individual opposition groups would be a very dangerous thing to do, but maybe it will have to come to that.