The problem is not simply that the kohain status is determined by birth and, as such, challenges our views of selection by merit. The further difficulty is that in the determination of the members of this important rank within the nation, we are actually unconcerned with merit . Even though our family connections will effect our lives, no-one would suggest that the determination of family love and connections should be based on merit and not birth. Yet, we respect citizenship determined by birth. Perhaps we are somewhat uncomfortable with this reality especially if it approaches nepotism, but we also respect that this is part of being a family and would be more disturbed by a parent that does not help.
Merit marks the individual.
When we evaluate on merit, we focus on the attributes and abilities of the person. Discrimination is deemed to occur when factors that are not tied to these personal attributes and abilities, specifically factors that connect this person to a group, are applied in situations when the individual alone should be considered. Inversely, when we do accept groupings not tied to merit, we are, in fact, placing group factors above the individual. Citizenship is based on birth. Citizenship by birth places the concept of country above the individual.