Makkot 9: Is Ignorance of the Law a Good Defense?

Are people responsible for doing the wrong thing when they thought it was permitted at the time that they did it, or to what extent is a person responsible for making sure he or she has knowledge of those permitted/prohibited actions? The example is a ger toshav - and the question of when punishing consequences kick in. That is, when does it seem close to deliberate, in contrast to the consequences all being left to God. With examples from the Torah where people were held responsible for transgressions they hadn't known they were committing (for example, Avimelech when he thought Sarah and Avraham were siblings, leaving her permitted for Avimelech to take as a wife - though she wasn't really). Also: 2 mishnayot - on the cities of refuge, and who can and cannot take refuge there. For example, a blind person cannot. An enemy of an "unintentional" killing cannot usually go to exile (and might be put to death for murder instead). Plus, the location of the 6 cities of refuge. Plus, initially, the killer ran to a city of refuge before the court judgement.