Maybe this software developer hasn't even tried his software on any of the "I'm my own grandpa"-structures. You'll find numerous variations of this story/song, e.g. Ray Stevens - "I'm My Own Grandpa"[^]. Wikipedia identifies Dwight Latham and Moe Jaffe as the ones responsible for the lyrics, but you can find the same story in numerous variations and on different tunes, usually referred to as a 'folk song'. So Latham and Jaffe didn't make it up from nothing; they just wrote down a song/story that was floating around. 25-30 years ago, I was checking out the genealogy programs available at that time. Several of them wouldn't even accept cousin marriage, and certainly not Abraham and Sarah (they had the same father, so they were half-siblings). Some people are very eager to condemn reality, because they don't like it. Personally, I want the software I create to be able to handle reality, even in cases were I don't like it.
Religious freedom is the freedom to say that two plus two make five.