I do want to clarify I do not say or believe "icons" are ugly. Icon's, since they are deeply religious, are in a different category, and so are more likely to be beautiful by the very fact they cause us to think of heavenly things not of this world. But Byzantine art in general (freezes, characters on jewelry boxes, wall paintings of saints, engravings on tombs etc...) lacks 3 dimensional natural human form and yes "ugly" is too strong a word. Perhaps "intentionally rudimentary" should be used instead.
How could a society steeped in Greek and Roman classicism simply give it all up and no longer paint or sculpt like they used to? The Church must have lobbied for this anti-realism. I reject the idea that for a thousand years no one wanted to make naturalistic sculptures or bascilicas that mirror Greco-Roman architecture--the heritage of their ancestors. It seems there must have been some new state-sponsored religious philosophy that restricted art and architecture into the abstract and "boxy". None of the ruins dating after Christianity became the state religion resemble ancient Rome or Greece, and I dare say, they look "inferior". Even Justinian's Hagia Sophia, as large as it is, still fits into the pattern of boxy and domed. Why the seeminly strict restrictions on art and architecture?
Christians used to imploy classical art style to convey Bible stories up until around the 4th century, so there is nothing inherently wrong with this naturalistic, classical style...yet it does seem when the Church was given full power it expunged this. Same goes for the West with its Midieval childlike paintings in books. Though at least they can claim Old Rome's culture was lost after it was sacked. Byzantines can't. So what happened?
Seems to me there are 3 possibilities:
1) The early Church (East and West) was filled with a lot of "iconoclastic" characters who were threatened by naturalistic classical art.
2) The Eastern mind is truly different and its artistic taste is simply inherently different than the West's. So when Constantine moved the Empire east, it jettisoned the Western culture and adopted the Eastern/Oriental.
3) Christianity, if followed to the tee, really does frown upon naturalistic art, and the Byzantines came up with a sort of compromise: abstract art.