Lalwende, you're absolutely right. What I
should have said:
The art that hasn't made it to our time has been lost for any number of reasons: fire, water, and carelessness are three that spring to mind. And there is certainly a lot of very good art that hasn't survived, whether for the above reasons or because of the low status and/or oppression of the artists (or for some other reason). In effect, we've often thrown out the baby with the bath water. But I think my main point still stands: even though we've lost so much art, good and bad, what remains tends to be good art.
EDIT: Having just read Fordim's post, I stand corrected. It's a shame--it
was a nice crackpot theory.