> some sort of 'Darwinist' view that some 'races' are more evolved than others.

The nearly universal European intellectual assumption at the time.

In other words, the collectors may have been racists, but they were not seemingly vicious racists. They simply accepted the prevailing unscientific ideology.

Since Child's interest was in "English and Scottish Popular Ballads," it's hard to see how any putative racial bias might have affected his choices or methods.

If he'd known more about "American Native Ballads," he might have included a (very ) few American items like "John Hardy" and "John Henry":   Anglo-American in form, if largely African-American otherwise.

But I believe Child died before texts of either song - not to mention "Frankie and Johnny" and "Stagolee" - could have been available to him.)