If you Shanghai people think you are very different from the rest of Chinese, go ahead and call yourself Shanghainese. When Americans call you Chinese, tell them you are not Chinese, but Shanghainese. I know one Hong Kong friend who alway insisted on distancing herself from Chinese. Talk about human psychology!
1. Han Chinese is obviously an ethnicity today. I have said nothing opposing this. What I am against, is your taking our current notion of Han ethnicity and applying it on history, and using it to judge and interpret history. That is unacceptable.
2. Compared to European ethnicities, the notion of a Han Chinese ethnicity is indeed relatively NEW, developed nearly from scratch during the last century, and refined and reinforced by the Communists in the last half century. Prior to that, you'd be hard-pressed to find abundant historical sources of identification to this Han ethnicity. Ethnicities are constantly changed and molded, but the English ethnicity in its modern or near-modern conception is far older than the Han Chinese.
3. To claim as you have done that Han Chinese is the "oldest ethnicity" is, indeed like I have said before, ANACHRONISTIC. You have provided no further evidence for your claim, but instead went on to attack me as a Shanghainese. You want to "talk about human psychology"? then what is your problem?
tianzhuwoye's reply below is very good, I would have written a similar reply, but he beat me to it.
The ‘Han Ren’ that the Yuan were referring to tended to be Khitan and Jurchens who adopted sedentary modes of life after establishing the Liao and Jin Empires. Today though, the Khitan and Jurchens are not Han (even if their states were ‘China’), and the Yuan term would now be called ‘Sinicized.’ ‘Han’ is a lifestyle. Today’s definition, like the definitions of all modern ethnicities, is a new one, designed to fit new purposes because things change. Ethnicity is always arbitrary and it’s too bad we don’t stop and think more often about whether or not it’s really worth getting as worked up about it as we sometimes do.
Just want to add to tianzhuwoye's post that the Yuan hierarchy system was based on geographic proximity and ally-enemy relationships. Those closer to the Mongols were ranked higher than those further away; those unconquered or were last to be conquered were ranked lower.
The idea of ethnicity, though superficially similar in some perspectives, did not exist then and that, Goujian, is my point. I'm not Communist-bashing, nor calling you a 乡下人 (Shaanwonin); there was no reason in bringing either allegations up in your rambling of a post.
We need to be careful not to exclude history and historical context when we talk about ethnicity.