This argument doesn't make any sense, because someone who somehow manages to find 'must' ambiguous would also find 'absolute requirement' ambiguous. The RFC doesn't solve the problem, if there is a problem in the first place.
If 'absolute requirement' is clear enough as plain English in a normal sentence, without having to capitalise it, then why isn't 'must' clear enough?
If 'absolute requirement' is clear enough as plain English in a normal sentence, without having to capitalise it, then why isn't 'must' clear enough?