This was a essay written in a brief time window for a "Manifesto Jam" in which we were asked to generate utopian/dystopian/impossible provocations for video games rather than a complete philosophical program or categorical imperative (in fact I have no idea how anybody would have come across this without that context). Treat its universalizing language/imperatives the same way you'd treat "Dada Means Nothing" or "Vow of Chastity" in the Dada/Dogme 95 manifestos, or "Skeletons Should Not Wear Armor" or "Never Apologize" amongst the other cohorts in the Manifesto Jam. It's a potential (personal) project you sign on to, not an edict from on high.
In any event, I think the Chesterton's Fence reference is not quite the right one, since I don't think either you or I are really confused about what HP is for (if anything it seems like the extent to which we think it is a load-bearing concept in video games). I would think the response to the "imagine how limiting hands are" argument would be "imagine ways of interacting with the world that are not bound by what hands alone can do" which would lead you to, you know, hammers and axes and tools and writing implements and so on. In short, thinking beyond the limits of hands here would seem to be a good thing for design (and there's probably an aside here about how many curb-cutting inventions were made by or for people with physical disabilities to exactly overcome the problem of living in a world where we design things almost exclusively assuming everybody has two equally dextrous hands).
In the same way, I think encouraging people to think of ways of rewarding or punishing players beyond incrementing or decrementing their HP (or something very obviously analogous to HP, like "affection points" in a VN, say) could result in some more interesting ways of designing and thinking about games. And yes, I am aware that there are games where HP is barely there or absent; as mentioned, I think Portal is an example of a good "HP-lite" game. It's in the engine and it gets impacted by entities, but it's more a timer to force you out of turret fire than anything. I think DF/Rimworld-esque city/colony management games also do an interesting thing with the HP-like element of the number of colonists/pawns/workers, where you lose if you run out of people, but 1) the people are more interesting than just existing as a number 2) there are infrastructure and gameplay challenges to having more people, beyond just a number to hoard.
If this doesn't give you any solace, then take comfort in the fact that I have absolutely no authority, influence, or power in the video game community and so even if you think the program laid out in the manifesto is dangerous and ignorant, nobody is likely to do anything about it.