This precedent setting argument ignores the fact that nobody is forcing you onto this fork, nor any future fork. You can choose to fork this time and not the next. Or to not fork this time and to fork the next. Either way, you will own whatever you had previously, but on both chains. You can sell coins on the new chain if you want and buy more on the old chain. Ultimately the free market will decide.
Discussion
There's already less than 21m coins in circulation, as many keys have been lost or coins burned.
Some bitcoin becoming dormant because of user-side key loss (which in at least some cases could in principle be recovered, e.g. landfill guy) or voluntary user-side burning is not comparable to some bitcoin becoming forever unspendable at the network level
In the context of your original statement: Much less important, but kind of related:" there will only ever be 21 million bitcoin” is a much cleaner economic coordination point than “there will only ever be 19.87 million [or whatever fractional number] bitcoin”
With regards to that ☝️it's the same. We already don't know how much has been lost/burned. It's estimated to be at least a couple of million Bitcoin. There will still be 21m if some are frozen, just like there are 21m even though some are lost/burned now. It effectively doesn't change the total coins. I would even argue that if the owner isn't bothering to migrate them to a segwit address, let alone a future QC resistant address, they're most likely already lost/burned.
>”Ultimately the free market will decide”
Agree, and that’s the point I’m responding to. My view is that “the market” will value credibility of supply schedule over an absolute number of outstanding bitcoin. Maybe Matt is right that the fork would retain sufficient credibility and would ultimately win out, but I don’t think that will be on the basis of having a marginally lower supply.
IDK how people will feel if/when _for_example_ President Baron Trump owns 1million of Satoshi's Bitcoin, because he's dead or burned/lost his keys. ¯\_(ツ)_/¯