In contrast to the far overused sugary definition, Phil Katz really was a rock star programmer. He also died a rock star's tragic and pathetic death.
There is probably no line between self and business for a guy like PK. At that time you could build a significant program or even a game singlehandedly. Most likely he obsessively made his better ARC program for its own reward (you could use it for free) and he was surprised both by the commercial success and the subsequent legal attack. Very personal indeed, and if he wasn't already a completely tortured soul, that would be more than enough to take away any shred of sense he had made of the world. Give enough cash and free time to someone who has been cracked like that and he quite easily can end up dead from an existential crisis with no practical boundaries.
Considering this was some 25 years ago now, if he thought about intellectual property issues at all, the mindset at that time was very reasonable in that your source code and executable was considered copyrightable like a book - it didn't matter if it provided the same functionality as someone else's program as long as you wrote the code. Just consider the fate of the original spreadsheet for confirmation of this.
To summarize, before you take any stand against the tragedy that is the life of PK, consider that there is probably a huge concentration of people very much like the early Phil Katz right here on HN. The man simply needed help, and he didn't get it.