But then we turn to welfare, and that’s where we make our great leap.
Improvements in welfare occur when there are improvements in utility, and those occur only when an individual gets an option that wasn’t previously available. We typically prove that someone’s welfare has increased when the person has an increased set of choices.
When we make that assumption (which is hotly contested by some people, especially psychologists), we essentially assume that the fundamental objective of public policy is to increase freedom of choice.
Our opponents have every right to contend that economists are unwisely idolizing liberty, but they err by saying we sail without a moral North Star.
The rest of the article is worth a read as well. It is an elegant and eloquent statement of one of the foundations of the microeconomics of welfare analysis.