why not set the default-option to 1?
then all mined blocks are irreversible and save
That would mean the chain would fork into 2 chains every few days spontaneously. Sometimes two different continuation blocks are found very close to each other and if everyone sticks to the one they got first, it means the network ends up split into two forks.
before the splitting: the networks has to decide: one is orphan and the other counts and is o.k.
when there are three, then 2 orphans, 1 o.k., whats the prob?
There is no "THE NETWORK" just individual nodes.
So if half the network (or some part of it) propogates block A and the protocol locks it and it can't change (the definition of a checkpoint).
The other half of the network (or some part of it) propogates block B and the procotcol locks it and it can't be changed (the definition of a checkpoint).
Now neither have of the network can reconcile w/ the other half. Part of the network considers block A canonical and part believes B is and neither will trust the other half.
You can't have a system that checkpoints blocks after 1 block.