I could argue either side of the equation. Some born into middle or upper class homes, get educated, make wise choices and lead good productive lives, while others born into the same environment fail because of poor choices. Children born to poor parents or especially poor single parents living on government subsistence usually repeat the cycle, while some can pull themselves out through hard work, education and good choices. All things being equal though, those born into the middle class have a much better chance to succeed than those born into economically poor environments.
Ah yes, the infamous birth lottery issue again. Maybe we can settle this after we all agree whether people should pay off their mortgages early or invest in beaver cheese futures.
Here's an example of why I don't believe the birth lottery argument:
Two children born out of wedlock, to two different teenage girls. Adopted less than a year apart by a loving middle age couple. Raised in a middle class suburb in a Midwestern city, both attended public schools, scouts, little league, etc. Both above-average intelligence, no health issues, parental abuse, etc. Sibling 1 ends up doing 20-to-life for armed robbery and has spent 80% of adult life incarcerated. Sibling 2 has a Masters Degree from a prestigious state university, and is doing well in the workforce. One chose to become a career druggie criminal, the other chose a career. Both made appropriate choices to get where they are today, it wasn't "the birth lottery"; they were raised the same. BTW, I know this family very well, this isn't a hypothetical situation.
I agree with your statement that "All things being equal though, those born into the middle class have a much better chance to succeed than those born into economically poor environments". That isn't going to change, nor should it. The folks who can offer their kids that middle class chance at success worked hard for it; we don't want to "deward" them in favor of those who made different choices that resulted in a different outcome. That's life; we don't all get a trophy just for showing up.
We need to give the poor the chance (via education and workforce opportunities) to make something better out of their situation, not make it easier to stay where they are (via failed multi-generational entitlement programs).
And I vote to pay off the mortgage early, BTW; beaver cheese futures are too risky if the government quits distributing it for free...