First, thanks to everyone for the great posts. Some really well articulated arguments have been made and my mind has been swimming all morning. (happily).
I also wanted to say that for me there are a couple of issues on the table. The philosophical and the practical.
Philosophical discussions and practical ones tend to get blurred for me on these threads. For me it is not theoretically impossible to separate the idea of ethnicity and the living of ethnicity.
I agree with the assertion that there is a larger metaculture to which we all have a duty. I think our idiosyncratic origins are extremely important (to us - to the individual) but on larger social levels there are (in my opinion) human and/or global issues that transcend an individual region, population or culture (such as global warming, nuclear warfare, international economics).
On a more esoteric level, there is - in my opinion - a human culture. Though the expression of human values may be different from region to region, culture to culture, they share many commonalities. Family, love, duty, sex, drugs, religion - they are all common themes throughout history, across cultures and ethnicities, and though the values may change, they are all different expressions of the same ideas. how do we live together? what do we do? for work? for fun? what do we believe in? how will we survive?
And let's not be naive, many cultures, civilizations and (what we would probably term now) ethnic groups that have "gone extinct" or been absorbed in a larger culture.
These definitions change.
Practically, it's a different matter. What an audience will accept and pay for is rooted in the philosophical, but can often be mitigated (and often is) by a plethora of other factors - from historical accuracy to historical awareness, to our cultural place and time, to our personal ability to be receptive to different interpretations.
Namaste