I don't think you can blame them for this. How many resources do you use without voluntarily paying extra above your legal requirements? Do you donate every time you go to free libraries, museums, parks, cathedrals, etc? I certainly don't and I don't think that makes me "the parasite class".
On the one hand I like the sentiment of paying for open source software. But on the other hand the free part of free software is kind of very on the nose.