If we do not trust open democratic elections to provide adequate representation for minority groups, then why don't we also have separate seats for Asians, women, Muslims, Fundamentalist Christians, old people, young people, computer nerds, and so forth? The absurdity of it becomes more obvious then, of course. But exclusive focus on ethnicity fails to recognize the multiplicity of each unique individual, and the many group "identities" under which they could potentially be subsumed.
Further, such segregation is antithetical to the ideal of integration that I have previously argued we should aim at. As David Farrar writes:
Dividing even more electors up on the basis of race is appalling... Labour's legislation moves NZ to a Fiji style country where racial quotas are enshrined. It is not the future I want for NZ.