> So what can be done about it? Can we prevent a person in the upper quintile (your typical HN reader) from feeding their child a balanced diet? Would that be fair?

Of course not, and no one sane thinks we should actively hamper development of upper-class children. The argument is that we can and should do more to provide additional opportunity to lower-class children.

> So we are not going to reach 80% mobility out of a quintile. We can't, without producing some sci-fi dystopia.

I agree we aren't likely to see that.

> But I think the article's presentation of 66% as a problem without much further elaboration is troublesome.

56%, not 66%. And I don't know what the ideal number is, either, but almost half of people born into poverty staying there does seem high to me. I suspect there's a lot more nuance that needs to be captured, too. We'd see 100% "mobility" if we simply swapped the bottom two quintiles, but that wouldn't actually address real mobility.