There is an implicit assumption in society and philosophy that humanity ought to be the basis of morality. But why do we believe this?
I find no reason to believe that humanity is of any moral value.
There are two main arguments I find people make to attempt to justify this idea. The first is rationality; the second is supremacy. I will not cover religious arguments.
First off, rationality: it is argued for any number of reasons that the ability to reason is the justification for human-centric morality. Possibly along the lines of the fact that humans are the only beings capable of understanding morality, and thus the only ones to whom morality applies.
This forgets that not all humans have an understanding of, nor the ability to act on, morality, and that some humans have a much lower level of rationality than others.
If rationality determines morality, then to include all humans, including those with mental disabilities, you must set the bar for inclusion low. Low enough that you begin to include other animals. Moreover, you can never be sure that this low bar will include all humans; to do as such, you would have to select the minimal level of rationality to be about zero. At this point it becomes hard to say rationality is of any importance at all, since far from saying that rationality is reason for humanity as a moral value, rationality only ever seems to exclude humans.
The other argument I have heard is that humanity is the center of morality, because humans are the ones who enforce morality, so they would naturally care about themselves. However, this argument risks justifying ideas we would find deplorable. The same line of reasoning justified early American slavery, because the slave owners were in charge and naturally cared about the color of one’s skin.
If we disagree with the second, how can we agree with the first? In either scenario, we are selecting a completely arbitrary trait and claiming that this forms the basis of morality. We have no greater reason to choose one over the other.
In conclusion, it makes no sense to say that humanity is the center of morality, since no argument can give a non-arbitrary justification. If it’s always some arbitrarily selected human trait that not all humans even possess, or which is not unique to humans in the first place, why care about humanity at all except as a merely biological category?
If we are to select a trait that actually forms the basis of morality, it should be sentience, the ability to experience pleasure and suffering. Because our ability to experience decides when we care. If something is to happen after our death, we assign it far less worth, and we go to great lengths to avoid suffering and pursue pleasure.
Humanity is a species of animal, nothing more.