Plasma is built on the condition that everyone is very compliant, but it is virtually impossible to achieve this.
Forcing the Plasma operator to put up a large bond can discourage bad behavior.
when there is wrong information in Root Hash, everyone has to quit
This is only true for the original plasma spec referred to as Plasma MVP. In Plasma Cash and Plasma Debit, there is no need for mass exits.
Plasma Cash: Plasma Cash: Plasma with much less per-user data checking
Plasma Debit: Plasma Debit: Arbitrary-denomination payments in Plasma Cash