The problem we face is that so long as people accept the moral responsibility of the US to police the world, inverventionists will always have the upper hand in this debate. When Kerry says that bombing Syria reduces the chances of Assad using chemical weapons in the future, it's really hard to argue with that, so long as you accept that the US national interest lies in stopping Assad from using chemical weapons.
The same rationale can be used to justify any possible intervention, including in Iran.
It is not hard to argue against that at all.
Few main options for Assad:
1.Assad is cornered by USA and starts losing badly and only possible path to victory is to use all his weapons on Israel, USA military bases around Syria and rebels.
2.Assad sees that he can not win and gives chemical weapons to Hezbollah. Hezbollah uses it on Israel.
3.Assad sees that he can not win and flees to Iran. Al-Qaedas first goal is to rush to chemical weapons and take it. They would do it without any problems. No one would dare to stand up against them since there would be chaos and those with weapons were fighting on same side with Al-Qaeda. Al-Qaeda starts executing Christians, Alaweets, Sunnis, Kurds. Later chemical weapons are used to start terrorist attacks all over the globe.
4.
Fairytale/best case USA scenario: They bomb Assad. Assad gives up and runs away. Non-existent or so far irrelevant pro western, democratic, civilized branch of rebels becomes most dominant and manages to stop Al-Qaeda and extremists, secures all chemical weapons, keeps Christians, Alaweets, Kurds and other completely safe and forms new government.
Next elections in Syria are in 2014. They seem far but maybe they are best chance for eventual peace.