It is not controversial (ie I agree) that the workers' and popular movements should be independent of whatever - big power or otherwise - ruling classes. We are not, as you seem to think, calling for Western intervention in Syria.
What appears to be at issue here is whether, if the account you believe of Houla is true, it fundamentally alters our assessment of the Syrian revolution.
Of course opposition forces, especially those fighting brutal dictatorships, often do terrible things. If, for argument's sake, it turns out to be true that it was oppositionists, not the Syrian state, which carried out that massacre, then that is to be criticised, even condemned.
It would remain the case that the overwhelming majority of deaths in Syria have been caused by the dictatorship.
I think you should consider the possibility that Barry's sources are correct, too. In that case, what you have been doing in this debate is, in effect (and I am not saying deliberately) acting as a propagandist for Asad.
As far as I can judge, it seems at the moment a) that any Western intervention is unlikely to even be on the scale of Libya, never mind Iraq, never mind old-fashioned colonialism; b) Western intervention would not change the character of the popular movement against Asad; and c) that Western imperialism has not created or stoked up this movement, it has its own sources and dynamic.