The researcher is not expressing ideology, but rather making a point about the issues of using productivity to assess public good.
His point is that by buying your tenth car you will contribute to productivity, but the use value of your tenth car is much lower than having those same ten cars (and thus the same productivity) spread across ten people.
It is even more obvious in the extreme case: if a population of N people produced N cars, the total public good of every person having one would (I hope you would agree) be higher than the total public good of one person having all of them for their own use. However, in both cases the productivity is the same.
Thus, whilst productivity is a useful measure, it does not account for everything we might be interested in when considering the effectiveness of our economies.
His point is that by buying your tenth car you will contribute to productivity, but the use value of your tenth car is much lower than having those same ten cars (and thus the same productivity) spread across ten people.
It is even more obvious in the extreme case: if a population of N people produced N cars, the total public good of every person having one would (I hope you would agree) be higher than the total public good of one person having all of them for their own use. However, in both cases the productivity is the same.
Thus, whilst productivity is a useful measure, it does not account for everything we might be interested in when considering the effectiveness of our economies.