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> Would open-source prevent this kind of thing? Probably.
I don't think I could have made the argument better than you have.
The point isn't that all closed source software does this, or even that most does it. The point is that when you cannot control the software, the abuse can happen. Anyone who has power can abuse it, which means that if you cede control over software in your router to Cisco, you have to trust Cisco not to abuse it. If you don't, then you don't have to worry.