You can't hard fork gold, either. You don't suddenly wind up with two copies of a gold bar because someone decided to Xerox your ledger to start a new one.
The scarcity of Bitcoins is entirely a cultural delusion.
And "BCH proper" has identical scarcity characteristics to BTC and it's not as if the creation of BCH negatively impacted the price of BTC - suddenly a new "scarce" token was created and everyone who was holding BTC before the fork is $1600 USD per coin richer today. The scarcity aspect is purely a social construct.
The distinction between "BTC" and "BCH" (and "BTCS" and "BCD" and so on ad infinitum) is cultural convention. There's no inherent technical merit (or alchemical nature) to one ledger over all other contenders, it's entirely a state of mind of its users.
Yes and no. Once the blockchain forks, the distinction between all those coins is very technical. Coins from one ledger cannot be spent on another ledger.
You're right though, cultural convention decides which blockchain is the "real" Bitcoin. Most people are using BTC at the moment, but Bitmain takes payment exclusively in BCH.
This might seem like a semantic quibble, but I think it's important. There will only ever be 21 million BTC, and only ever 21 million BCH. If Bitmain decided to charge 22 million BCH for their latest ASIC miner, nobody would ever be able to pay that bill regardless of how many forks there are.
For a blockchain fork to have any value whatsoever, people need to want to own it. Bitmain ASIC sales are driving demand for BCH. Every other Bitcoin fork is doing rather poorly.
Forks aren't diluting the value of BTC, because people know that BTC is the real asset. Everything else is like fool's gold.
There is no intrinsic property that makes it "the real asset", it is a completely arbitrary distinction based on social coordination not on any fundamental property of the ledger.
"the relative abundance of asteroidal ore gives asteroid mining the potential to provide nearly unlimited resources, which would essentially eliminate scarcity for those materials"
Apparently with the lack of a strong gravity like Earth's to sink down heavy metals, they are way more accessible in smaller bodies like asteroids (Ceres and Vesta maybe?)
Even this could change if the miners and thought-leaders decide that it should.