The OP contains a video of a debate involving Sam Harris.
Harris is a moral realist, he believes that there are moral facts about the world that science is best equipped to investigate.
He bases ethics on the quest to increase the well being of conscious creatures.
In his book "The Moral Landscape" he describes a condition that could be called the worse possible suffering for everybody. Morality is about moving up from that deepest of all valleys in the Moral Landscape.
It is possible to be mistaken about morality. It was once thought that slavery and misogyny was morally good. We were wrong about that. It turned out there was a better way to organise society that resulted in increased well being for more people. The Taliban think it is good to keep half of their society uneducated and dressed in a black bag. They are wrong. We should not excuse this sort of error on the basis or cultural relativism. It is not up to personal opinion, nor is it a matter of preference or might-is-right.
I highly recommend the book, it is the most lucid and compelling argument against the myth that you "can't get an ought from an is".