When I first heard about someone being "grandfathered in", I (incorrectly) assumed the analogy was "old people are senile and can't be expected to adapt to new

When I first heard about someone being "grandfathered in", I (incorrectly) assumed the analogy was "old people are senile and can't be expected to adapt to new laws, they get a free pass". That is, it's modeled on an exemption for (those old enough to be) grandfathers, not based on who you have as a grandfather. And thus, if anything, is a smear against the old rather than black people (or grandmothers). With that said, as others are noting, it does, for some people, evoke the Reconstruction-era practice, so is a bit more complex than it might seem.