Why do people have no concept of aesthetic harmony in ecclesiastical buildings?

The Princeton University chapel, while not especially old, is conventionally attractive and well-conceived. It looks, in point of fact, like a church, and a much older church than it actually is.

The bones of the building, then, are lovely. Which makes me all the angrier that they have hung these psychedelic vomit banners in the nave. I spent much of my undergraduate career planning accidents in which they would disappear in a mysterious conflagration.

Now, these banners are hideous in any context. They are vaguely abstract, they are asymmetrical, and the only reason that they have any colors that match anything at all is that the stained glass is pretty lavish. But these banners also have no common aesthetic heritage with the chapel. They're just modern and ugly and incongruous.

Handsome Gothic churches are special in that they need very little in the way of extraneous décor. They certainly shouldn't be saddled with modern and revolting monstrosities.