I like that, I think I'll use it next arguement with my lefty sister.
Presumptuous assumes some knowledge, with added rudeness - but fatuous ignorance presumptuously uttered is the oafish drivel of the truly brain-dead - i.e., the perfect description of leftist discourse.
Describes every lib I've ever talked to. Describes their prevailing attitude that anyone who doesn't agree with them is stupid. Describes their charge of "anti-science" when they haven't studied the opposition's analysis of the evidence (evolutionists, this is you).
Another perfect example, the other night, my libinlaw was talking about Gingrich - "I don't care how brilliant he is, he's a buffoon."