It (moral culture) is a prime example of covert circular reasoning.
True Moral Capital could only be established as being measurable, if there was such a thing as an accepted moral median, by which and to which all other acts could be compared and measured, the ethic equivalent of 0 degrees centigrade, below which things are less moral and above which thing are more moral.
However, most medians are measure of energy or matter, things that demonstrably axiomatic, tangible and measurable, they are objective in the true sense of the word.
Morality and ethics are not; they are both abstract and very, very subjective.
Therefore, Moral capital would have to be based on something similar such as "cultural capital".
Cultural capital is based upon a perceived and flexible set of phenomena derived from artistic cannons, legal principles, and accepted social norms the general underlying principle of the concomitant civilization.
Typically, these are boiled down to simple aphorisms such as

1. Might makes right
2. Compassion trumps all
3. Creativity is better than destruction
4. Improvement of well-being is desirable
5. The state is more important than the individual is
6. The individual or family is the foundation of the state

These are then judged as good or bad and made in to the median morality of the time, however each of these good or bad is open to corruption by focusing on one aspect of society and universal application, to make them not the median but the baseline AND the border that must not be breached
For example and respectively, the above can be made be seen as

1. Social Darwinism and eugenics
2. Victim culture
3. Societal brain washing
4. Ultra capitalism
5. Totalitarianism
6. Anarchism

Once this is established, we have as you say, the absolute moral line, which is morally right absolutely and is thus become ineffable, making the act of critiquing it an obviously immoral act.

In the words of Richard Nixon "Well, when the president does it, that means that it is not illegal."

That is as old as Jesus character the victim of wrongfully being prosecuted and hung on a cross crusified as a guilty person punished to death but an innocent person.