I agree with him about network effects and I want to add something here about switching costs. You might join an messaging service because of network effects (you want to talk to the users who are already there), but you *stay* because of switching costs.
If you quit a service, you quit the friends who use it. If those friends matter a lot to you, then the service operator can do pretty terrible things to you (like invading your privacy) and you'll still stick around.
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Multiprotocol clients like Pidgin attack those switching costs head on, letting you escape a service provider's walled garden and still pass messages to the people who aren't ready to leave yet. Not only does this make your life better, it makes their life better, too.
Because when it's easy to leave a service - when the switching costs are low - the service has to worry about losing users, and that limits how badly they can abuse the users that stay behind.
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