> a free, rights-protecting nation has no basis for an agreement [between any two or more states] with a dictatorship that routinely violates peoples' rights.

Wikipedia quote: "States and non-state actors may choose to not abide by international law, and even to breach a treaty but such violations, particularly of peremptory norms, can be met with disapproval by others and in some cases coercive action ranging from diplomatic and economic sanctions to war."

I think isolating bad actors can be a limited solution to the absence of physical power/not wanting to start a way, which ultimately as you rightly state corresponds to a situation of absence/breakdown of law that is best avoided.