As the Wiki says, scalping is well attested at the Crow Creek site. It has also been documented everywhere from Sand Canyon Pueblo in Colorado to Chavez Pass and Grasshopper Ruin in Arizona, to Kodiak Island in Alaska, and to various sites in the Great Plains.

Your friend's view was outdated decades ago, but he is certainly not alone. Many revisionist scholars (Peter Hassler, Victor Montejo, Vine Deloria...) have argued that archaeologists and antrhopologists, when reporting violence among prehistoric indigenous groups, are simply partaking in the colonialist conspiracy to justify European atrocities, continue oppression, dehumanize native tribes, and devalue indigenous culture. They are well-meaning, but adjusting data to fit a romanticized past will not end well no matter how good the intentions. Beth Conklin has some good words to say on this in her book Consuming Grief: Compassionate Cannibalism in an Amazonian Society: "when the gap between rhetoric and reality is revealed," indigenous and Western relations can only be harmed. In my own work, I find that warfare in a culture's past only humanizes them more: how can we ever come to true understanding if we believe in the idealized myth of different communities that got along peacefully for thousands of years?