It seems pretty straightforward to me. Wealth redistribution has this positive effect: If you take $1000 from a billionaire and give it to a very poor person,

It seems pretty straightforward to me. Wealth redistribution has this positive effect: If you take $1000 from a billionaire and give it to a very poor person, total happiness increases. It also has a negative effect, high level of redistribution can inhibit production. The optimal level of redistribution depends on what you're optimizing, it's usually a mix of societal happiness and some notion of fairness. (I personally would want to optimize happiness and prosperity.)