The best counter argument when someone quips "there's no evidence that large theropods had feathers" used to be "there's no evidence that they didn't, either."
Now, there's this.
It's very difficult for humans, even some scientifically-minded ones, to recategorize objects in their brain space. For most humans, dinosaurs, especially large theropods, have always been essentially big demon-lizards, and it's hard to wrap our minds around the idea that, in fact, were they alive today, they would certainly be regarded wholly as birds, not as a distinct group.
While cladistically, the phrase "birds aren't dinosaurs, dinosaurs are birds" is wrong, it's much more correct for describing what dinosaurs actually were. Not ancient reptiles* that happened to be the ancestors of birds, but ancient birds that happened to be descendants of archosaurs.
*Oh yeah, and there's no such thing as a reptile.