To wilfully take life away is wrong. It may be a justifiable wrong in certain situations, such as self defence or in defence of another. The state of Syria, has not sent violence against the USA. Actions which destabilise the Assad government destabilise public goods supply. Further violent action by the Arab Council, Russia and other foreign nations intensify and polarise the situation.
Chemical weaponry in Syria was disarmed without a violent coercion, why not approach it all like that? Dropping bombs on Daesh / ISIS for ignoring human rights is hypocrisy. It is wilfully taking away life, and it does not deliver the substance of human rights. Killing the executioner of infidels does not allow the infidels free practise of religion. Assaulting the Daesh / ISIS group for creating a bad political system does not create a good political system.
Much support for action comes from fear of Islamic extremism. It is a risk and a problem which can strike beyond the places where Islam is most concentrated, however, when it strikes away from it’s homelands, it strikes feebly. More people die from food poisoning in France than have died from Islamic extremism. It must be known that the most common victim of Islamic violence is a Muslim. When the USA intervenes it does not do so from a moral high ground, the money spent on war would be more honourably spent on curbing death from food poisoning. This perspective is found in those who lack awareness of the political groups in the region (Assad, ISIS / Daesh, Shia militia, Kurds, and more).
To support the war is to support death, disease and dismemberment. If moral justification is sought by Human Rights transgressions, than it can only be maintained by supplying the public goods lost by the transgression. More violent action from a multitude of foreign nations will not inspire trust in the honour of those nations.