This is not true. As I said to Roger - you might think circles are beautiful. I think they're ugly! Explain to me why you consider them beautiful.
This answer will be a philosophical one. There is a reflective process going on. I know this upsets you, because for spurious ideological reasons you hate the word, but it shouldn't. Science and philosophy are not mutually exclusive.
No, it doesn't upset me. And I don't hate the word "philosophy" (words are my business -- I love them). I just find the practice of philosophy useless.
Anyway, if we want to answer the question of why one animal finds circles beautiful and another doesn't, perhaps philosophy will come up with some sort of answer. I don't know. I can't imagine it would be very accurate or reliable or satisfying.
Doesn't matter, tho, b/c this thread is about a scientific approach.
I don't think we have the means of answering that question at the moment. But to get there, we might follow a process like this:
First, figure out what goes on in subjects' bodies and brains when they have the experience of perceiving things as beautiful, ugly, or neutral.
I'd be willing to bet that there are telltale physiological responses and signature neurological responses associated with that state. It's likely that some of these will also scale with the intensity of the experience.
Then run some experiments exposing subjects to various types of circular items and patterns, as well as other types of items and patterns, and measure their responses, as well as have them indicate somehow "beautiful", "ugly", "neutral".
Interview the subjects while showing them the same sets of images or objects again to determine what kinds of associations their brains conjure up when they see these things. You might even run the same measurements to see how their bodies and brains react while they're describing these associations.
In the end, you might discover that subject A (me) has a brain which tends to have more frequent and stronger experiences of beauty in general, triggered by a wider range of objects, and that this is due to A's individual chemical and neurological makeup, and that A has many happy memories associated with balloons, wading pools, merry-go-rounds, and Twister boards.
You might also discover that subject B (you) has a brain with a different composition that has fewer and less intense experiences of beauty, triggered by a narrower range of objects, that B responds negatively to regular forms in general but positively to more chaotic and nonlinear forms, and that B has very bitter memories of a childhood spent in a Spanish Franco-era housing project with lots of regular features, but wonderful memories of later years spent in the Alps with his grandparents.
That's how you'd get a scientific answer.