Stallman is actually less (ethically) invested in the freedom of works of art than he is about practical software tools. He probably wouldn't like Steam's DRM, but I don't think DRM on games is capable of imposing the same kind of subjugation that he sees done by companies who produce tools which are more strictly necessary to the lives and livelihoods of their customers.
Although I'm not a proper Stallmanite, I do see a powerful ethical dimension to the motivations for producing free software (and free culture as related to education). I don't see anything evil in the minimal kind of DRM imposed by Steam, and although I would praise any game company who opened the source code to their engine, or Valve if they opened the source code to the distribution system itself, I don't feel compelled to condemn game companies who don't do so. Those are my two cents, for whatever they're worth, as someone intellectually and ethically committed to the principles of free software.
(I wouldn't call it a religion for me because my views about the importance of share-alike copyright licenses, like the GPL, are grounded in other principles that could yield different prescriptions when applied in novel circumstances. But I do often do things make the choice to use free software out of principle, even where technically superior non-free solutions are available. You decide if my views are radical enough to for me to speak on behalf of the subset of the F/OSS community you'd like to address.)