Criticisms of Zuckerberg's donation debunked

Those are not 'debunked' but rather 'addressed.' Some of the criticisms are still valid, but the author chose a different reference frame.

Consider “Mega-philanthropy is non-democratic, because it involves a few individuals shaping the future”. The re-framing is 'as far as we can tell from his statement at least, they plan to use the money to alleviate disease, improve education, and fight poverty' which are 'unequivocally good'.

I reject this reference frame. Consider the move towards charter schools, which is funded in part by the mega-philanthropy of Gates. Set aside even the question of if charter schools 'improve education'. Charter schools are anti-democratic.

Public schools for the most part are run by local schoolboards. Remember, education isn't only important for the student, it's also important for businesses who want to hire new graduates, infrastructure which assumes a basic level of literacy, and a political system at least nominally based on the idea that educated citizens are better than uneducated ones. So even if I have no children, I should still have some say in how the school is run, because the results of the schooling will affect me.

A charter school, on the other hand, limits that decision to the owners of the school and (indirectly through parental choice) to the parents.

This is anti-democratic, because it removes political power from most citizens.

Now, we can talk about balance - should we remove some democracy in the name of better education? But to do that, what is "better education"? Is it test scores? Is it the local school board which gets to decide which is best for the community, or the state? How much influence should mega-philanthropists have on getting to decide what constitutes "improvement"?

If billionaires have a bigger voice than tens of thousands of citizens who have a different view of what is 'good', then that too is clearly anti-democratic.