If some groups don't feel a certain solidarity and identity, who don't feel like they're in the same boat as the principal group, democracy doesn't work. In extreme cases, that kind of exclusion has led to some of the worst excesses of ethnicity. Rather than threatening the integrity of a nation, inclusiveness may prevent violent and ultimately self destructive ethnic nationalism. Some have demonized ethnicity, because in certain cases, such as in the former Yugoslavia, the creation of a people and a nation leads ultimately to ethnic cleansing. But these unfortunate cases do not amount to a condemnation of the ethnic dimensions of a nation.
Ethnic nationalism is an unavoidable fact of life.
But to remain viable, it can and must incorporate many identities.