1/ Bitcoin or an altcoin’s fixed supply is far more than simply its code. The key is *how easy* this variable is to change.
2/ If an increase/decrease can be forked in, it can be forked out. The very fact that monetary policy is open for discussion is a threat.
3/ The strength of bitcoin’s supply limit comes from a combination of factors:
4/ a) Node sovereignty - regardless of whether a minority or majority want to change the supply, myself and others can always choose to personally maintain what we consider to be the optimal monetary policy.
5/ b) Ideology - could also be referred to as “social contract”. The more people that understand/believe in the sanctity of an unchangeable monetary supply, the less likely they are to accept changes to it.
6/ c) Culture - overlaps with ideology above. Precedent is extremely important. If the supply has been changed before, it means it’s something we can debate and argue over. It will always be under threat of change.
7/ d) Economics - participants in the system have strong incentives to resist any increases in the supply, which would immediately devalue their holdings. Non-participants may have opposite incentives, but they have no influence on the system.
8/ In summary, the strength of bitcoin's scarcity is not based on a parameter within the code, which as @truthcoin says, is very easy to achieve. Instead, it's derived from both the physical (nodes, hardware, network structure) and social (culture, ideology, economic).
9/ These properties are *extremely difficult to replicate*. None of the existing altcoins look like they are close, least of all Ethereum (increasingly node-lite network; total lack of any coherent ideology; bad precedent; governance-heavy).
10/ As the understanding of the personal and societal advantages of sound money grows, and waves of gimmicky altcoins continue to fail, I have no doubt that we'll eventually see attempts at "soundcoins".
11/ Either through releasing new alts, or repurposing existing ones, these will compete on their "soundness" credentials. But they'll be way behind by that point, for the reasons stated above.
