If everyone were given equal opportunity to achieve good outcomes for themselves, the only way we could end up with inequality of outcomes is if people choose to have worse outcomes than others. But why would anyone ever choose bad outcomes?
People try to explain this by saying some people are "lazy" or "impulsive" and thus make suboptimal choices, but does this really make sense? If a significant portion of society is consistently making suboptimal choices, are there societal changes we could make to convince more people to make better choices?
If we think there are societal changes we could make that lead more people to make better choices, then can we really say those people had "equal opportunity" to make those choices before the change?
And if we think there aren't any societal changes we could make that lead people to better choices, then what we are saying is that there is inevitably some portion of people who will not achieve good outcomes within our system. And if that's true, is it really a good system for humanity as it exists?