I'd say it depends upon how you define "capitalism" because most advocates of "capitalism" define it as an economy of free and voluntary exchanges while most of its detractors define it as an economy of giant corporations that oppress their workers and buy politicians to protect themselves from competition. The staunchest advocates of "capitalism" and its staunchest critics ironically tend to share the same hatred of corporate welfare and monopoly. Both are usually all for the little guy selling goods and services.

Just like with "socialism", most discussions about "capitalism" are actually people with different definitions talking past each other. I'd say the important issue in economics is monopoly vs anti-monopoly not "capitalism" vs "socialism" and free software is definitely on the side of anti-monopoly.