That's just the personal side. By having different identities at my various services, I limit to the extent possible what each entity knows about me. My bank needs no information about my other bank accounts, much less my music purchases or where I shop. Yes, some of that information leaks across providers, and there's a whole industry to discover and bring together the data so that providers can try to sell me more stuff or insurers can find ways to deny coverage. Some employers do that too to filter out candidates. The more online services we use -- which is how the world is going -- the more traces we leave for such discovery and collection.
Some services, such as Facebook and Google Now, even get people to sign in so that their activities can be explicitly tracked, creating a single profile across all those aspects of you. The promise is intelligent agents that will figure out what you want for you, but that convenience pales in comparison to the hold such services will have on you once they decide what you want -- and cut you out of the decision completely. (The European Union gets this, even if the U.S. doesn't.)
Fortunately, despite what you see in TV dramas like "CSI," police agencies can't quickly figure out your profile and whereabouts through computer searches, though they have forensics technology and access to credit card usage and cell phone records with minor effort. But as more of your aspects are cross-tabbed and federated through a common ID, the possibility of these police-state scenarios will increase -- and it won't be criminals alone who can be so easily monitored.
The heterogeneous nature of both our personas and the contexts in which we operate makes a single identity scary. The tendency is to collect all that in one place or at least provide a single key that opens them up. Yes, theoretically any such unified identity could create separate buckets that compartmentalize our aspects, even require explicit permission for services to open other buckets. But you know how that will work: Governments and service providers -- who pay the bills, after all -- will demand broader access "just in case." You won't be able to manage who you are to whom.
Even if you could, that's a lot of explicit work few people will do. Just think how few people organize their email or address books or, say, the spare keys for their neighbors' and friends' houses. Forget about using the privacy settings on your computer or smartphone, whether or not they're available. By default, everything will be open for exploitation, like at Facebook and Google Now, which count on users' tendencies to share. Massive studies have shown they're justified in those assurances.
I don't have an answer to the problem of too many accounts and passwords. But I know that it is not a single identity.
This article, "The dangers of a single identity," was originally published at InfoWorld.com. Read more of Galen Gruman's Smart User blog. For the latest business technology news, follow InfoWorld.com on Twitter.