hackula1 means this: If one child is born to the family of a billionaire, and another child is born to a poor unwed teen mother, then in what meaningful way can it be said that those two children have "equal opportunity"? Even if the billionare's child is a lazy fuckup, he/she still stands to inherit hundreds of millions of dollars and so will never have to want for anything. Even if the teenager's child works hard, without access to nurturing child care, education, books, etc., the odds are stacked against that child leading a happy and successful life, much less becoming a millionaire.

The only way to make it truly be the case that those two children succeed or fail in life due to their own qualities and choices -- "equal opportunity" -- would be to take the billionaire's money and spend it equally on nurturing and educating the two children. (In the US, the "estate tax" is a tax on inheritance, that is, it's our society deciding how good or bad it is if a child can inherit all or some of a parent's fortune.)