> they don't have any money on the other (main) chain because it was already spent
Right, the double spend attack. It's feasible under certain circumstances, such as a chain split. That doesn't mean the system breaks down completely, but that it has to be mitigated. In the event of a multi hour long network partition, some participants are likely to take action.
> they would have the incentive to follow the partitioned chain and promote the forked software because their money doesn't exist on the main chain
My point was that their money do exist on both chains as long as transactions are replayed. That may be more or less hard depending on the nature of the split (say, a whole country falls on the Internet completely). Economic participants do have an incentive to replay transactions (for example by following the satellite feed, or a number of other ways).
It is enough that one participant does this to at least give everyone else the possibility to mitigate themselves. Not a good situation to be in, of course, but still. It doesn't require nodes to follow both chains, and certainly not promote minority chains. There is simply no economic incentive to do that should transactions be guaranteed on both chains.
Right, the double spend attack. It's feasible under certain circumstances, such as a chain split. That doesn't mean the system breaks down completely, but that it has to be mitigated. In the event of a multi hour long network partition, some participants are likely to take action.
> they would have the incentive to follow the partitioned chain and promote the forked software because their money doesn't exist on the main chain
My point was that their money do exist on both chains as long as transactions are replayed. That may be more or less hard depending on the nature of the split (say, a whole country falls on the Internet completely). Economic participants do have an incentive to replay transactions (for example by following the satellite feed, or a number of other ways).
It is enough that one participant does this to at least give everyone else the possibility to mitigate themselves. Not a good situation to be in, of course, but still. It doesn't require nodes to follow both chains, and certainly not promote minority chains. There is simply no economic incentive to do that should transactions be guaranteed on both chains.