The Itsme idea has a few big downsides.

Itsme is an enormous project, on a trans-societal scale.  Tens of millions of  things, especially doors, gates, and Points Of Sale, will have to be retro-fitted with electro-mechanical locks, embedded computers, and networking; throughout society: in homes, public infrastructure, and enterprise.  It will be expensive and take years.  Some societies will simply decide not to do it - too expensive, too intrusive,... 

Yet, before it becomes practical for people to give up their hard copy in favor of the digital life nearly all "doors" must be converted to be Itsme-smart.  Until then, people will have to carry both Itsme and hard copy.  As long as the second and third worlds aren't converted people will still need to keep hard copy for travel there.  For these reasons alone, Itsme may remain little more than a fantastic dream for generations to come.

When people hear about the idea of moving all their important tokens into one place - their Itsme-mobile - they get nervous.  Never mind they've had them in one place before: their wallet or purse;  Itsme seems kind of vulnerable.  This can be dealt with.  You can wear a little transceiver - e.g. in your watch - which warns you if ever you leave your Itsme behind someplace.  Itsme-mobiles know where they are, so they can tell you where to find themselves.  If stolen, they are virtually worthless, because a thief could never duplicate your biometrics.  Besides, you can call your Itsme from a friend's, and tell it to die altogether.  Nevertheless people still get nervous.

The same goes for Itsme-websites.  If I put my house deed into a website, what would happen if the computer or disk crashed?  An Itsme advocate can of course ask: what happens to the deed in your file cabinet if your house catches fire?  Indeed, ultra-reliable database farms already exist, in which data is the safest it's ever been in history - far safer than in your home. 

What about thieves and spies?  Can they steal or emulate my Itsme-identity,  or snoop and  vandalize my Itsme-website?  All modern digital commerce, whether on private lines or internet, relies on nearly impregnable security. The same minds that invented television, the transistor, the computer, and the internet cannot fail to invent totally impregnable security, and soon.  Then, your identity and documents will be far safer than ever before, not less safe.

Carrying around a device that broadcasts the fact that "It's me" all over the place seems to be the end of privacy.  Wal-Mart has started putting RFID tags in merchandise, and that has started a remarkable paranoid backlash where people think enterprise and especially the government will be able to track them everywhere they go and divine what they're doing, without their consent.  Itsme will have considerable privacy controls, and Near Field Communications has a range of only a centimeter, but will people believe it?