It is a tradition that tries to keep the breed pure, without crossbreeding diseases among family members. In this way, the same diseases are not transmitted from generation to generation and duplicated.
It seems to me that the elders in your community know what they are doing by maintaining this custom.
Although it may seem cruel, it is a way of preserving themselves as a community.
The bad thing is that they resort to violence if those affected do not comply, it means that they go with all their might to avoid the crossing of blood.