Assad's propaganda has been very effective in the West. Makes Goebbels look like an amateur. Presumably Russia and Iran have been helping.
That the Ghouta CW attack was a rebel false flag attempt was one of their ridiculous lies that the gullible in the West believed.
Hopefully this particular mistruth will be nailed today with this Human Rights Watch report:
Syria: Government Likely Culprit in Chemical Attack | Human Rights Watch
22 pages of forensic examination.