Voskuil expressed concern that checkpoints could be used to control the "true chain" and suggested users validate the full chain without checkpoints and select their own checkpoints to apply the optimization. However, Wuille noted that this may not be realistic and proposed getting rid of checkpoints altogether. They also discussed buried softforks, which modify the validity of a theoretically construable chain from invalid to valid but are unlikely to result in a reorganization due to the vast number of blocks to rewind. They agreed that the proposal for ISM checks for BIP34 and BIP66 is not a security feature but a reasonable choice for code that likely won't affect the valid chain again.