It's a good thing unless your entire worldview is wrapped up in having your children "do better than you," whatever that means. I think many people have a gut reaction to decreased mobility (I know I do) as being somehow anti-meritocratic. It's very possible the science doesn't back that up but I don't know that there is any research on it. I feel like high mobility in both directions means a society is more meritocratic than one in which you generally stay in the same socioeconomic strata you're born into.