In this thread I am mostly referring to ethical intuitionalism, mostly concerning whether there are objective facts of morality. I guess my most basic case would be to look at slavery. How does one concede some rational intuition of morality when slavery was an acceptable way of life previously in early human history? Is the idea of morality something progressive and continuously changing, or is it something that is merely static?
As far as I can tell, the basis in the way humanity regards morality is based on successful evolutionary strategies that tell us that certain forms of social cohesion are better than others. Hence we have concepts like love, loyalty, friendship, tribe (whether that's your football team fan base or the nation you live in), inhuman other, etc.
One interesting thing to note is that when people dislike other groups, primarily ethnic groups, they also tend to believe that this group is somehow less than human. See the long history of this sort of regard against black (throughout out history), Chinese (the old west being a good example), Mexicans (in our modern day), Jews, Japanese, and Germans. You can see, for example, any number of war posters from the 40s as showing Germans as less than human. There were whole branches of science devoted to showing that the white man was superior in the 1800s and early 1900s as well. It all leads to a central idea, dehumanization. If one believes another is less than human, than they are not as worthy of love, respect, kindness, and esteem, making it easier to commit violence against them and excusing the hater of their hatred as justified.
This again goes back to the concept of morality as a survival strategy, humans like to band together to form tribes, nations, cultures, governments, social systems (and they seem to enjoy making social systems more complex over time, but hey, nobody said biological drives were always a winning strategy, they work until they don't), ethnicities, etc. The close kin you fee to someone, the more likely it is you will treat them kindly and with more humanity.
Personal morality works pretty similarly actually, from what I can tell, but thats outside the scope of this discussion.
In terms of an absolute right or wrong, whether it exists or not, there are probably multiple absolute right and wrongs, depending on which philosophy one ascribes to. One philosophy has one set of absolutes while another has another set of absolutes. But the world of ideas and real world human behavior are very different things.