It seems like there's usually another layer of reality below the one which seems to be fundamental.
Nice to know that the fundamental theorem of software engineering applies to the design of the universe too.
The issue is not people customising their own install of Kodi. The issue is custom *hardware* set-top boxes being sold on eBay or Marketplace or whatever, which are explicitly advertised to run Kodi (which is preinstalled) and have the capability of pirating content easily (thanks to the not advertised custom addons).
People think it's Kodi "vanilla" which allows the pirating since they don't realise it's thanks to the custom addons, so the reputation of Kodi suffers.
Promising costs nothing, it's the delivering that kills you.