The argument is again and again that the value of Bitcoin will increase because supply is limited to 21 million. But this is quite simply wrong. Every time Bitcoin is forked that is in real terms an expansion of the Bitcoin currency beyond 21 million. To some degree the same is true of alternative crypto currencies which will flood the market. There is already more than 1000 cryptocurrencues (
https://en.wikipedia.org/wiki/List_of_cryptocurrencies )
Why is the foking affecting the btc supply? The number of btc issued in the market has been fixed from the beginning, and initially it was distributed free of charge, so in the exchange market, it was trading at a loss of 21 million btc. so btc exceeds 21M seems impossible, even if there are 100 or 1000 altcoins. btc is only held in different places but can not be lost or increased.