These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Anvilicious: "The Guilty Party", which states that an upbringing in ghetto-type places, coupled with having parents who are abusive or just plain neglectful, will lead you down a less-than savory path.
Heartwarming Moment: at the end of "A Retrieved Reformation", a cop is able to positively identify a notorious safecracker who he has been chasing. However, observing that said safecracker was willing to sacrifice his freedom by using his abilities to rescue a little girl, he pretends not to recognize him.
Values Dissonance: A Harlem Tragedy is about a woman being proud of her abuse at her husband's hands, because she says it shows how he's interested in her and how he always buys her things to make up for it later. Of course, given the generally satirical tone of the story, this probably isn't meant to be taken seriously.
Also, O. Henry was racist. Really racist. So racist as to make a "comical" reference to dousing black people in gasoline and burning them to death (although the term he used wasn't "black.")
Tear Jerker: Most of his stories are humorous, but some, most prominently The Last Leaf and The Furnished Room, are quite tragic.