Very good points, yes. Stage 5 and 6 are individual and rarely develop, and none of it is a one size fits all, as vygotsky's sociacultrual theory proposes, a persons cognitive development and how they put meaning to things, concepts and actions form from thier environment, society and culture. What we see as good or bad is dependent on our respective cultures, and can be easily hypocritical. Psychologically is a very intresting field because we dont have a definite answer on most things, the mind is textbook subjectivity.

We are taught the 6 stages of moral development not as a fact but to provoke thought on moral development in context of concrete operational thought (Which itself has shown to be subjective) and how our modern psychological understandings stem from. however the first two stages give a fair idea of pre-concrete-operational moral reasoning, so we can better negotiate reason with children.