For as long as I can remember a strong cohort of technologists have agitated for identity portability between internet services. Their theory goes that individuals should “own” the reputation and identity data about them stored inside platforms and be able to take that information with them between services. They believe portability will empower users, encourage more platform competition and lead to better services.

Many smart people I’ve had conversations with lately are excited that blockchains provide—at long last—the key technology to unlock data portability. These people think that blockchains can enable trusted “memory” to be distributed across a network rather than warehoused and maintained by specific companies or organization inside walled gardens.

To these people I say, be careful what you wish for.