Adulterous relationships. Incestuous relationships. Relationships between professors and students. Relationships based on economic or employment coercion. Relationships in the workplace, even if not coerced, that could result in favoritism prejudicial to others. Again, consent merely distinguishes rape from non-rape. There are many degrees of wrong and unethical conduct short of the outright criminal.

Some of those are fair points (scenarios issues involving external people), although considering the context of this discussion I was referring to ethical concerns between the two parties involved in the relationship. Coercion of various sorts negates consent in my book.

I’ll add to the list: doctor-patient, lawyer-client, judge-lawyer, judge-litigant, social worker-charge, police-detainee, prison guard-prisoner, etc., even in contexts where there is no actual coercion. There is more to relationship ethics than consent. You have to consider the ethics in the context of the other relationships between the parties. Lawyers engaging in relationships with their clients is in fact an ethical violation, regardless of consent, because of the possibility of or appearance of abusing the lawyer-client relationship. Relationships necessarily also affect third parties (other partners, coworkers, etc.) Those effects must be considered too. People owe each other (not just partners, but third parties) more than just not committing rape.