Public sentiment is that contentious chain splits are bad. This is probably because they have potentially disruptive consequences, where users can be potentially confused by the split, and because they may reduce confidence in the coin that split, because splits represent conflict within the community. Users can be easily confused by a split not because it is inherently confusing, however, but because of the way our wallet softwares do not treat them in an a standard, reasonable way. And the decrease in confidence only comes from how we, culturally, tend to perceive and react to disagreement and conflict. But even given the generally negative sentiment about conflict, certainly most would agree that avoiding it altogether has potentially much worse consequences than addressing it, and that a healthy treatment of conflict is usually best for everyone.

In the case of Bitcoin, that point is highlighted especially by the Bitcoin Scaling debate. When some developers suggested an upgrade to the Bitcoin network allowing for larger transaction throughput via a larger blocksize limit, some developers for the most popular Bitcoin client, Bitcoin "Core", were opposed to such an upgrade. In spite of attempts by the former group to at least make the upgraded software available to the community so that the disagreement about whether such an upgrade was a good idea could be played out via the mechanism built into the network (that is, via nakamoto consensus, where those investing in the system vote with their proof of work to create the longest chain), social media manipulation in the form of astroturfing and censorship prevented resolution of the conflict by those healthy means. This did not, of course, resolve the conflict itself. Instead, it only kicked the proverbial can down the street a little longer, and led to an even bigger confrontation later on. That "confrontation" ultimately occurred when, instead of providing their upgraded software as an alternative to the current software and trying to upgrade the entire Bitcoin network (with which their success had already been limited by social media manipulation), developers in favor of the upgrade were forced to implement their upgraded version of the software with "replay protection", where, by default, transactions made in their upgraded software would not be valid on the other side of the chain split, and vice versa. Instead of trying to "upgrade" Bitcoin from the inside, they split the chain cleanly in two, effectively resulting in two distinct currencies with a shared history. It's important to note that doing so was not their first choice. It was a last resort.

Given the social and political situation (and the imminent activation of SegWit), resorting to implementing replay protection on their upgraded software was understandable, and probably the safest move. Many were desperate to make sure that a version of Bitcoin that functioned as it was originally intended continued to exist. In the context of this "new" separate currency, currently referred to as "Bitcoin Cash", however, it is important to consider the potential for contentious chain splits in the future without replay protection, and to consider the healthy role they have the potential to play in allowing for nakamoto consensus to work most efficiently .

Before considering those things, it may help to review what actually happens in a contentious chain split. While some are now familiar with the idea of one blockchain based currency becoming two separate currencies, as happened when Bitcoin split into BTC and BCH, what happened more specifically was that, before that point, there was a single state of the Bitcoin network, as reached by nakamoto consensus. After the split, there were two states of the network, each governed by what we may still call "competing" implementations of the same general protocol. They are the same, at the very least, in that they are both secured by proof of work via the SHA-256 hashing algorithm, and each side is competing for that proof of work, given each's value and the profit driven nature of mining. Because they are directly in competition with one another in terms of proof of work, you could argue that BTC and BCH are still part of the same network, and that the split has simply not yet resolved itself into nakamoto consensus. Such a resolution would occur when a large enough majority of the hashrate commits to one chain so as to leave the other chain effectively worthless, both because of its vulnerability, and because of the resulting low value feeding back into its lack of hashpower.

Because of the replay protection in the case of BTC and BCH, no transaction on one side of the split was valid on the other, even though a user might have control of the "same" coins on both sides of the split, controlled by the same private keys. This meant that users were forced to value each side of the fork separately the moment it happened, and actively do something in order to interact with the BCH side of the split (since it was the side that implemented replay protection). Without replay protection, the lines between the two sides of a split are fuzzier. A transaction remains valid on both sides of the split as long as it is only involves coins that exist on both sides. In fact, it is impossible to actively prevent a transaction that is valid on both chains from being propagated to and mined on both chains. The only coins that don't exist on both sides of the split are those that have been mined since the split (or those that have been mixed with them), since, of course, different miners will have mined the different blocks on each chain.

One might consider the situation without replay protection to be an inferior one because of the ambiguity of the situation and the applicability of most transactions to both chains. Given the right infrastructure, however, that ambiguity and mutual compatibility can easily be converted into greater convenience and choices for users.

Below are my thoughts on how those negatives might be turned into positives.

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Given a mechanism by which users' wallets can alert them to the existence of a chain split (perhaps with a threshold of estimated split hashpower as reported by nodes, so that one person running an S3 in their basement can't get everyone's attention with their "chain split"), that user could be constantly made aware of exactly which of their coins exist on both sides or one side of the split. It would be trivial to show the value of those funds given the current market for coins on each side of the fork. They could also be notified about whether the coins being sent to them are on both sides or one, and be given the option to auto-convert coins they receive on only one side of the fork to an equal amount from each side (ideally via one of several competing services). Additionally, they could be given the option to mix their coins with coins on only one side of the fork (as a service probably provided by exchanges or miners) if, say, they decide that they want to sell their coins on one side of the fork, but not the other, or if they want to transact with someone else who only wants to accept coins from one side of the split.

The above services and standards would give one the option to not decide which side of the fork to support in the case of a contentious chain split. Such a situation is highly preferable to forcing users to make a decision when they might not have an opinion at all. Given a chain split where it's understood by most users that two protocols are competing for nakamoto consensus, it might even become the norm to not split your coins unless you have to. (How many users will really understand the intricacies of all potential future forks enough to confidently bet on one side or the other? I imagine very few.) Merchants may also be more likely to list their products' prices in the equal-amount of combined coins from both sides of the split, since many of them will also not know enough to take sides, and will want to play it safe by remaining neutral. (The extra volatility from the split would probably be not much worse than crypto experiences in general, and may actually be less if chain splits become more common place, where the value of the two combined tends towards the value of the coin before the split.) If a customer wants to pay with coins from only one side of the fork, then a conversion would be required given the current market, and the merchant could auto-convert back into equal amounts of both sides of the split if, again, they want to remain neutral.

Given an ecosystem where the above features are standard, a user could potentially continue on indefinitely after a chain split without being forced to make a decision about the split with which he or she is not comfortable . The market can then be made instead by those who knowingly and purposefully are taking sides in the split. The automatic conversion for neutral users could halt when a user specified (or standard) condition for the split "resolving" is met (probably also having to do with hashpower, but maybe also taking price into account if the user wishes). Such a resolution may happen in a month, a year, or maybe never. Of course, the longer the two forks co-exist, the more likely it is for the user to become informed enough to "take sides" and then sell the coins from the other side of the split, thereby becoming a market maker themselves, and helping to resolve the split! Also, the longer the two forks coexist, the more likely that the majority of coins in circulation will have become tainted, slowly forcing the slowest of deciders to at least treat each side of the split completely separately.

Compared to the situation that was forced to take place (and is still taking place) involving BTC and BCH, the above seems, to me, to be vastly superior and more streamlined for users. Neither side of the fork is in any way the "incumbent" side. Users can, knowingly and by default, transact on both chains to remain neutral and, in the event of one chain's death, still have effectively the same transaction history! In the case that they do want to take sides, "tainting" services run by those with access to new coins allow them to.