If morality is about what people do, then why it does it really matter how "objective" the reason behind why we would do something is?
Morality is more about what people
ought or
ought not to do or
should do or
should not do. This is the ought of moral obligation.
It is about assigning value to certain acts, labeling them as
good or
bad,
right or
wrong.
Why does it matter? This is more of a personal position I hold. It matters to me for several reasons, but you may not care one bit.
Quite simply, if morality is based solely upon the opinions of human beings, then there is nothing that obligates me to prefer a particular morality over any other except my own interests.
If morality is objective and based on the commands of a Good and Just God, then I am obligated to live a certain way and if I fail to do so, I am guilty and will be called to account for failing to live as I know I ought to have lived. For example: I would be obligated to love my neighbor as myself and if I failed to do this, I would be guilty of not living how I should have lived. I would be a transgressor. I would be a "law-breaker".
So it seems to me it matters a great deal.
All things are permitted if there is no immortality and no God to judge us for our deeds. We become gods in determining what is good and bad, right and wrong.
But if we are immortal and if there is a God to judge use (something I argue is the case) then we do not determine what is good and bad, right or wrong, but morality is something discovered, not invented, just like any other law that we discover.
It matters to me a great deal because if moral values and duties are objective, then moral relativism is false. I do not want to live according to what is false, but what is true.
Once again, none of these may seem significant to you and you might not care if God exists, or if morality is objective. There are some apatheists who do not care whether or not God exists.
So whether or not something "matters" seems to me to be an issue that is subjective. Nor would I really try to convince you to believe that these subjects matter if you are not of the opinion already that they matter.