You should be afraid of having the social graph of half of the Western world on Facebook. You should be afraid of storing most people's email unencrypted, in only a handful of data-centres.
Then there is the progressive lockdown of the whole internet, where it becomes increasingly difficult to speak your mind, simply because it's harder and harder to get your own blog. I mean your blog, on your ___domain, hosted by yourself (or at the very least a virtual hosting provider). These days, it's Facebook, Medium… places where an overseer has the right to block whatever you write. A good thing in most cases, but at least we should be able to speak elsewhere.
What in the world does a locked down internet have to do with being able to control the code that your own devices are running? It's a tenuous connection at best, but if people really believe these are somehow connected then it would explain some of the odd (to me) resistance I'm seeing in this thread.
Take package signing in Linux: package managers check the provenance of the code before installing it. If this were extended to executables, users would have the benefit of a GPG trust chain, or have to indicate to the system that they want to trust new code before running it.
This is not related at all to the walled gardens. Even though technology could potentially be used to build walled gardens, it doesn't have to be. Just because technology could be used for bad purposes as well as good purposes does not mean that the good purposes should be avoided, does it?
Walled garden is a general trend whether on the web or on devices such as the iPad and game consoles.
Such control have advantages, but it facilitates abuses. It even requires some of them: if Apple allowed interpreters to run 3rd party code, it could introduce a loophole that may create the equivalent competing store. Massive online sandbox games face a similar problem with the ability to build arbitrary stuff: they generally don't want their player to build or draw… inappropriate depictions.
All this is not really a problem as long as it stays confined to a specific purpose (such as playing games), or a specific community (such as here). Inevitably, curation means control, enforcement, and lock down. We need that.
What scares me is the gradual disappearance of free, uncontrolled space. Both online and on devices. Walled gardens used to be confined to game consoles. Now they start creeping up on general purpose computers. The iPhone and iPad where a significant step up. And now even the desktop isn't safe. The iStuff made it acceptable to lock everything down in the name of the safety and convenience.
We are losing the war on general computation.
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Besides, there is a link between the freedom of the network, and the freedom of the devices. Without free software, you can't have a free internet: people will just used the (proprietary) software that's available to them, and that software will naturally steer them to "safe", controlled online spaces. You quickly get a cyberpunk dystopia where you have to break the law, perhaps even risk your physical safety, to run programs not approved by some corporation on your device (if they're still officially yours by then, and not "leased" forever or until you look at them funny).
And of course, without a free internet, you'll have a hard time organizing and implementing free software —especially if the software is susceptible to free the network free again —it will be shut down as "unlawfully facilitating circumvention" or something.
The simultaneity of the gradual locking down of both devices and network is no coincidence.
You should be afraid of having the social graph of half of the Western world on Facebook. You should be afraid of storing most people's email unencrypted, in only a handful of data-centres.
Then there is the progressive lockdown of the whole internet, where it becomes increasingly difficult to speak your mind, simply because it's harder and harder to get your own blog. I mean your blog, on your ___domain, hosted by yourself (or at the very least a virtual hosting provider). These days, it's Facebook, Medium… places where an overseer has the right to block whatever you write. A good thing in most cases, but at least we should be able to speak elsewhere.