Invasion is not yet justified.  Invasion is an option of very last resort, especially when dealing with a country of such strategic importance such as Syria.  Invasion is an option of last resort because of the collateral damage it necessarily leads to, the impediment on sovereignty it entails and the escalation of conflict it entails. It’s the nuclear option that is reserved for the very last resort due to the severity and unpredictability of its results.  With regards to Syria, we simply aren’t at the point of last resort yet. The UN hasn’t even levied sanctions against the Syrian government yet [1] , never mind frozen Assad’s assets, tried negotiations or mediations, assisted domestic opposition groups or applied strong diplomatic pressure beyond a general condemnation.  The danger you expose the citizens of Syria to combined with the unknowable outcome of an invasion means that it simply isn’t justified to even consider invasion until all other means have been exhausted, which they haven’t been.  [1] "Syria: UN Human Rights Committee Condemns Crackdown." BBC News 23 Nov 2011.