Just because some despised minorities exist today, doesn't mean they will continue to exist in the future under CEV. If a big enough majority clearly wishes that "no members of that group continue to exist" (e.g. kill existing gays AND no new ones ever to be born), then the CEV may implement that, and the veil of ignorance won't change this, because you can't be ignorant about being a minority member in a future where no-one is.