Not many people are capable of fixing their car personally, but they do benefit from not being required to go to Toyota whenever it breaks. Nonfree software is like an appliance which you're legally forbidden from modifying without permission from the original maker.
They could always hire other programmers to do that. And there's real value in having that option, or getting software from a community that works like that, most famously the Linux distro scene.
Actually it is pretty irrelevant how many non-programmers are capable of compiling or meaningfully editing the C program. The point is that a programmer cannot (reasonably) edit to restrict you freedom.
However, after rethinking what I wrote, I should clarify that while the underlying principles are the same regarding what RMS is trying to do here (limit programmers to protect users), the GPL has nothing really to with this particular fiasco.