If the point of a non-personal, universal or group-level, morality is to satisfy group level values, such as equality and justice, then the justification for coercion is that co ordination is necessary to achieve them, and voluntary co ordination is not sufficient.
If the point of personal morality is to achieve personal values, there is no justification for one person to impose it on another with different values.
Its not about how good theories are but what they are supposed to do.
If the point of a non-personal, universal or group-level, morality is to satisfy group level values, such as equality and justice, then the justification for coercion is that co ordination is necessary to achieve them, and voluntary co ordination is not sufficient.
If the point of personal morality is to achieve personal values, there is no justification for one person to impose it on another with different values.
Its not about how good theories are but what they are supposed to do.