“could be” and “probably is” are two very different claims. Which one are you making?
The original basis for the trait was either a mutation, or more likely the combination of the effects of several mutations. However, its establishment throughout the human population was almost certainly due to selection.
Again, it almost certainly persisted throughout human populations as they spread globally due to selection. If it wasn’t selected for, you would expect at least some human populations to have lost the trait due to random chance, founder effects, and genetic drift.
Why not, exactly? Please spell out your reasoning.
Fair enough, but that’s not skepticism, that’s merely uninformed opinion.
‘Ubiquity’ isn’t a good description of pubic hair. Almost every adult has it, yet its still has a lot variance among individuals and populations, and total absence is very rare. That’s not proof of a ‘beneficial’ trait, but it it doesn’t provide support for a ‘neutral’ trait at all.
Defining ‘neutral’ can be pretty difficult by itself. Hair in the groin may have no apparent benefits to modern humans who keep it covered up, but our ancestors had no clothes at some point in the past and it may have great benefits for them at the time. It may have been a trait developed after we began to wear clothes, and it somehow helps control body temperature or protects from disease in clothed humans. Then it might have been an neutral trait in the past that became beneficial.
As for a compelling explanation, well I need convincing that any human trait is not related to sexual selection, especially the traits that are adornments of our genitalia.