If you can't modify the software (or have no concept of what source code is) these freedoms largely become meaningless.
I hear this again and again, and I think it's absolutely false. It's like saying
"I don't have the time to shop around for the cheapest product, so a market economy is useless to me"
In both cases the point is that even if you don't have the time or the knowledge someone else does, and only a small number of such people are required for the system to bring benefits to everyone.
There may be auxiliary benefits from the freedom that are granted to others. But we're not talking about those benefits, we're talking about the freedoms _you_ have. I'm not arguing that there aren't other benefits, I'm arguing that pratically speaking in both situations your freedom is primarily limited by your lack of knowledge of the situaiton, not by whether the software is proprietary or not.
Oh come on. Many people I know don't vote because they think (correctly) the time they spend will be much better spent doing something else.
That doesn't mean the freedom to elect a democratic government is not valuable to those people.