It is not clear that the Assad regime used gas. It would not be unheard of for the jihadists to kill there own people, so let the UN finish its investigation.
There is no historical precedent or other reason the believe that a military strike will deter the government actions. In fact historically intervention of this type has increased the pace of civilian deaths.
There is no clear goal other then retribution for an attack, which while appalling, is not against US citizens.
There are many places we could spend time and money with non-military aide at home and abroad that would better serve the interests or US and humanity.
Let the UN inspectors finish their work then act according to international law.