Here's the article:
march 6, 1867, Indiana Herald
A fellow named Wiley accidentally shot his brother, inflicting a serious wound. He was engaged in the pastime of shooting a negro and missed his mark.
1867 would be post slavery (13th amendment was ratified in 1865). Even during slavery, for all of its vileness, killing a slave in the US could result in murder charges (google turns up numerous cases, pre- and post-civil war in the US - e.g. this article from 1864 Richmond (probably Richmond, Michigan, since it was in an Ann Arbor paper)). While I'm not trying to diminish the horrible history of race relations in the US, I'm a little skeptical that someone could have a pastime of shooting at (free) blacks without serious legal repercussions.
Could someone explain this?
First, shame on Harper's for not quoting it correctly. The actual article is from the Indiana Herald and states:
A fellow at Milford, Kosciusko county, named Wiley, on last Tuesday, accidentally shot his brother, inflicting a serious wound. He was engaged in the Nasbylike pastime of shooting a negro, and missed his mark.
The important part is actually the "Nasbylike". From the archive:
David Ross Locke (born 1833), " Petroleum V. Nasby," like Browne, began life with the varied but uneventful round of printer and editor. He was engaged for a time as compositor, and later as reporter, for the Cleveland Plaindealer, with which Artemus Ward was also associated. The second letter over the signature which made him famous was published in 1861 in the Hancock (Ohio) Jeffersonian. It was a mock petition against the negroes, osten- sibly drawn up by an ignorant secessionist, and its satire was so telling that it was copied all over the country. Later efforts in the same line won for their author reputation and considerable in- fluence.
The entire Nasby "arguement" is here. (If you are sensitive to purposefully racist remarks that, in this case, are pointing out the folly of racism, I would suggest not clicking the link.)
Basically, Nasby was a byword sort of like we would say "man on the street interview" meaning for some numbskulled answers to basic questions today.
There is a lot of nuances in the statement that are hard to explain because race relations weren't just black and white back then. Anyone that wasn't a White, Anglo-Saxon, Protestant (WASP) was a second class citizen. The largest mass lynching in the US was of Italians. Irish really did have to face need not apply signs. Then there are also the Chinese and the Indians. The idea of race relations being "White people" and "Black people" is a very, very recent idea.
With that said, the article in question is making an off hand remark not meant to be taken seriously. It would be like saying someone tried to get a Darwin Award by offing their brother followed by "You're doing it wrong!" In this case, the author is basically saying that shooter is engaging in a mock shooting and it backfired.