I've heard that argument actually used when the crimes of the soviets would be too much to ignore... yes, but they aren't true marxists...
After the horrors of Soviet, Chicom, NVA, and Cuban atrocities became too glaring to ignore, the cry went up among liberals:
“TRUE SOCIALISM HASN’T BEEN TRIED YET!!”
In its present form, used to excuse Muslim barbarism, it goes,
“THIS IS NOT ABOUT ISLAM!!!”