make a blanket statement

To make a general statement about a large group of different people or things that is typically lacking in nuance and accuracy. A: "All teens hate school. They don't actually want to be here." B: "That's a little reductive, isn't it? You'll have a hard time connecting with your students if you make blanket statements like that." Leave it to Uncle Ned to make blanket statements about the "fools" who don't share his political beliefs.