What do you call a person who expresses strong opinions on things they know nothing about? [duplicate]
I think you need two words to capture the contradiction inherent in the type of person you describe. So, given that, how about arrogant ignoramus?
Arrogant (M-W): exaggerating or disposed to exaggerate one's own worth or importance often by an overbearing manner
Ignoramus (M-W): an utterly ignorant person
I also like SteveSliva's suggestion of uninformed blowhard, which is in the same vein as arrogant ignoramus.