It's not an argument at all in that sense, it's a counter-argument, to the claim that it doesn't matter if a test is racist since the alternative is "worse overall". I was pointing out that having a test be racist can be equivalent to being worse overall.

It also assumes that people will vote their own interests. Kids and the mentally ill presumably will not, so it doesn't apply to them. And it assumes we care about benefiting them (and therefore that we care when a candidate is worse for the whole population including them); in the case of immigrants and possibly felons, we don't.