Why should the license model of the source code prevent developers from making a living? Why should companies which release their software under proprietary licenses also be the only ones able to profit from it?

As Stallman said: Think free as in free speech, not free beer.

Interesting. In Spanish there is libre ("free" speech) and gratis ("free" beer). Now that I think of it, libre is part of the name of many linux packages (Libre Office). Never made that connection before.