A morally relevant difference

I noticed muddle used this phrase to justify why some are not treated equally with others.

All three words--morally, relevant, and difference are subject to definition and can certainly be interpreted in many ways by many people.
Morally means deciding what is right in a case.
Relevant means bearing on the matter at hand.
Difference means the way one person is identified when compared to another.

I think a better simple way to define when something is a right might be:

whether or not everyone gets "enough."

If I feel very ill I should be treated by a physician whether I can pay him or not.

If I am eating adequately a balanced diet, then I have no right to a big steak unless I can pay for it.

It is not difficult nor does it require a philosopher to explain it.