Ultimately, there's no such thing. A blockchain is simply a data structure that keeps you from editing it in place by changing old entries. If we agree to rewri

Ultimately, there's no such thing. A blockchain is simply a data structure that keeps you from editing it in place by changing old entries. If we agree to rewrite it, we agree... And some forks are done simply by having the majority of the clients (or processing nodes at any rate) agree to make certain things invalid. Such as an attacker's loot address, etc. The chain is all there, unedited, but no longer has the same effective meaning. We really need a community that rejects these proposals the same way they'd reject photocopied money.