Apologies to the @moderators if this thread is becoming too “stream of consciousness” for this forum as I (once again) make a move towards answering my own question, but a possible solution occurs to me:
Proposal: Non-cruelty is the guiding principle of Buddhist politics.
In such a thought-system, my example in the OP of non-cruelty as a universal value becomes something of a special case, as all other political questions reorient towards that north star.
To take abortion, the suttas do recommend “abstaining from the taking of life and encouraging others in undertaking abstinence from the taking of life” (AN 4.99). So, in this example, some reasonable restrictions on abortion (counseling about alternatives, a short waiting period, etc) might be taken as “encouraging others” to not kill whilst more severe restrictions (e.g. making abortion a crime) would cross the line from “encouragement” into “cruelty” and thus become unacceptable.
Taking non-cruelty as the north star has further implications. For example, suggesting that a woman could carry the baby to term and then put it up for adoption is perhaps a reasonable suggestion in some cases, but might itself be cruel if (for example) your country’s adoption system actively harms children or is in the middle of its own crisis (not to mention the cases where even carrying the child to term would itself be harmful to the woman in question in some way). In these cases, the focus on non-cruelty would point us towards also addressing the foster care system and the opioid crisis as intimately related to (interdependent on) a compassionate response to unwanted pregnancies. More broadly, it suggests that such counseling should always be discretionary and situational (and never legally mandated).
So we can see how a focus on non-cruelty puts a specific bound on the domain of the law: the law should (under this ideology) have the role of enumerating the many ways that humans can be cruel and of outlining humane and appropriate responses to said behavior.
Of course, people who previously had the privilege of cruelty (e.g. American police officers) might claim under such a rhetorical structure that the taking away of that privilege is itself cruel. Others might contend that zero sum political problems afford no “non-cruel” solution. But I think these issues are red herrings. It’s obviously unacceptable for police to use their authority to inflict needless harm and even zero sum problems admit fair (if unsatisfying) solutions (e.g. a coin toss).
In fact, I think the focus on cruelty helps to clarify these thornier issues somewhat. For example, the privilege enjoyed by police or the existence of radical economic inequalities are seen (in this system) as themselves unproblematic: they only are problematic to the extent that they allow legal cruelty: a clear opportunity for legislation.
Does this answer jive with others’ understanding of both 1) Buddhist ethics and 2) political theory more broadly?