f I start a new blockchain tomorrow I am under no obligation to give anyone anything.

This is not traditional for blockchain forks. Normally the history of the chain is consistent up until the fork. Even if one is going to fork to their own hacked historical record which removed rewards from certain accounts, then should they not also erase all content from said accounts which may be bringing value to the new chain. No obligation of course yet ethically they seem like vindicitive school boys.