5. Syria can stop this, but the cost to it stopping it is higher than the cost of letting it go on.
I disagree with this assessment.
Syria wants a "legitimate" excuse to come back into Lebanon. World-wide disapproval forced them out after the assassination of Hariri. They would like nothing better than to come back in and be seen as the "liberator" of Lebanon, once again.
Lebanon is the lowly pawn in this chess game. And totally expendable, in everyone else's eye.