It's a programmers dream.
It's not a software problem. Or at least, it's not purely a software problem. For the vast majority that freedom would make no difference. They don't know how to change things anyway. I remember a few months back on here when we were going 'Why don't people use PGP more? Oh yeah, the interface sucks.' And did anyone change the interface? Nope, not to my knowledge at least.
Did any of us make better encryption tools, despite there being available encryption libraries? Not to my knowledge.
That sort of freedom is tied to your capabilities as much as it is your tools. If your understanding of a computer goes something along the line of 'that magical glowing box under the desk.' it makes no difference either way.
To get to real freedom, in the sense that Stallman seems to mean, requires more than a change to open source software, it requires a system be built from the ground up to not just enable but also encourage co-evolutionary mastery. And it's not clear how that would work. Having the source code of the system available is probably a part of it, but you also need people to be able to start off with simple changes using the same language that the system is described in - preferably they'd use that language at least to some degree to instruct the system to do basic operations.
A lot of that probably has to do with how modular you can make a program - when you make changes how much of the program do you have to hold in your head to understand their effects? And I think that's probably, ultimately, a processor architecture level decision if you want it to be how most things on the system work.
Looking at it from the software side: at the moment, even with open source software, sure you can theoretically go in and learn about the program and make alterations and ... but that is not a trivial thing to do. Even for people with deep knowledge of computing it's not a trivial thing to go and learn about how the program works, and if they don't already know the language it's even worse. There are loads of open source projects out there at the moment where what needs to be done is essentially obvious but there's such a lack of people with the abilities and interest to do it.