One of the hardest questions about what is going on in Syria is the political character of the paramilitary groups. There are countless numbers of them including those trained & armed by the CIA & US special forces; there are mercenaries & foreign fighters from Iran, Hezbollah, & elsewhere.
Assad supporters describe them all in the Muslim-hating & war-mongering language of the US Pentagon. It’s a fundamentally racist attitude toward groups who they revile to defend Syrian & Russian bombing of civilians.
As operatives for the US, Iran, Hezbollah, they are a treacherous crowd but they are not all “throat-cutting jihadists” as Assad supporters call them. Nor do the militias represent the scope of the popular movement against Assad’s dictatorship. They are not bombing cities only to kill the militia fighters but to destroy the popular opposition to Assad–as the Saudi-US-UK coalition is doing in Yemen.
Their presence & activities in cities do not justify the bombing of civilians. By one estimate, Aleppo has 8,000 militia fighters but 250,000 civilians live there.
My knowledge of the militias is insufficient & I have found no reliable sources but this article by a Syrian revolutionist, once a political prisoner & now in exile, discusses the development of these groups in a political way & takes it out of the realm of Islamophobia, fear-mongering, & demonization.