How can one respond to those who perceive an absence of justice and equality in some Sharia rulings, such as not killing a free person for a slave, questioning how to convince them that the blood of all people is equal and there is no difference between a free person and a slave, or a male and a female?

According to the majority of scholars, a free person is not killed for a slave. Islam is a religion of civilization, justice, and equality, and it has regulated interactions among people. This worldly life is a realm of trial and testing, and the righteous servant's reward is multiplied. Equality and justice do not mean that people are equal in all things, for Allah Almighty has made distinctions among them. A Muslim does not rule his intellect over Allah's rulings except to the extent that he understands them, and his duty is to submit and surrender to them, for Allah Almighty is the Wisest of Rulers and the Most Knowledgeable concerning the welfare of His servants.