Splitting a currency unit into two does not dilute the currency any more than moving the decimal point does.
In order to dilute you would need to create new units and issue them to someone other than existing holders.
Well mining does create new units, doesn't it? And instead of having +6mn coins, you then have +12mn due to parallel mining of +3600 coins on each fork.
No difference than moving the decimal still. Miners will mine in proportion to the market value of each new coin which means the share of supply held by each existing holder and each miner who spends a given amount of resources on mining will remain the same.
Or to put it another way. If 75% of the total Bitcoins are now mined and held by existing holders, then 75% of the
total of GregBitcoins and GavinBitcoins will also already be mined and held by existing holders. So again there is no dilution of any existing holder.
Regarding existing holders, if you have your own keys you are relatively ok (minus the obvious destruction of USD value), but the situation with coins in online exchanges and wallets will be "problematic" if say an exchange with 500k BTCs, say 'ok my clients, now you have 500k BTCCs because we adopted this fork' (and we are keeping 500k BTCs of the other fork for ourselves). It would be like stealing BTCs and exchanging them for Gavincoins.
People need to do a bank run in every exchange (maybe even online wallets too) well before we reach the point of the hard fork, to ensure that they have control of their BTCs.
Yes, there are infrastructure issues and issues of fairness with respect to third party custody. Although likely irrelevant now, Cryptsy had something in their Terms of Service that
explicitly gave them ownership. That's nuts.
Very real issues, but not the same as dilution.
