One of the main reasons that Western governments have had difficulty getting support for military strikes against Syria over the use of chemical weapons is that the public don't trust claims about WMDs made by our leaders. This is because the claims made about WMDs in Iraq turned out to be complete bullshit.
It should have been known in advance that Iraq could not possibly have the resources to have a viable WMD programme that posed a threat to anyone- their wealth and technical know how was simply not enough.
However this principle when applied to Syria makes it abundantly clear to me that the Sarin gas attack on a Damascas suburb must have been carried out by the Syrian regime not the rebels as various people are claiming- including the Russian government.
Weaponising sarin effectively is clearly very hard to do. Consider the Tokyo subway attacks in 1995- despite the gas being released in a very confined space and thousands of people being exposed only 13 people were killed. This was after an attack that had been prepared by scientists belonging to the cult. Yet supposedly it's a toss up as to whether an incredibly effective open air attack that killed hundreds was carried out by a ragtag assortment of rebels or by the regime that has been running a chemical weapons programme for forty years. It isn't.
That is not to say that we should intervene in Syria- the rebels contain elements that are very dangerous- but there is no serious doubt that the Assad regime fired Sarin into a civilian suburb to massacre hundreds of innocent people.