Another excellent essay from this author, but more specifically we need an undeniable ethic: a rule to govern our actions involving other people (in any way), the validity of which no one can plausibly deny.

Respect for the capacity of other people to choose for themselves is such an ethic. It follows from the simple fact that human beings have no choice but to effect choices. That makes choosing integral to being human: to respect a person's capacity to choose is to recognize that being's humanness. All that boils down to a handful of absolute prohibitions: no killing, harming, coercing, stealing, or manipulating (which includes lying, cheating, etc.) in effecting any choice (taking action to bring a choice to fruition).

Interestingly, since the example of the couple in the article concerned informed consent for all involved, her conduct would not violate that ethic. Still, in a society governed by this ethic freedom would be the result of people respecting one another's capacity to choose, not some mythologically ideal state of being that people are supposed to pursue as their primary goal in life. It does not dictate the ends people are to pursue, but it is all about focusing on one's effects on other people in pursuing one's desires, whatever they might be.

If curious for more about the ethic, "Can't Get Any Simpler" is a "3 min read" here in Medium with links to articles about that ethic from various perspectives (for the sake of 'guest readers': nothing I publish here is behind the paywall).