For the past week within the Phoronix Forums has been a very active thread entitled Is Valve's Steam antithetical to Linux and the very core of the open source spirit?
The thread has sparked dozens of responses. The original poster's views are that Steam is anti-ethical to Linux because developers must sign an NDA not to discuss their Valve contracts, Valve has some say over which games are distributed/promoted, control over some game pricing, reduces rights of the game developers, etc.
The poster is also not happy that the code to the Steam client is not open-source and that it uses proprietary protocols. The DanLamb user says, "Valve wants Steam to take away rights of Linux developers." He concludes, "I don't seen any positives out of this for Linux."
Fortunately, most Linux gamers don't see this way as Steam being a detriment to Linux. Valve supporting Linux has been the most significant boost to the Linux desktop in many years, perhaps ever. Most of the complaints expressed in the thread are just because Steam is closed-source software. Sure, it would be great if Steam was open-source software, but it's not, yet Valve is doing much good for Linux -- both directly and indirectly.
Among the positive Linux activities that come to mind this Sunday morning include Valve promoting and embracing OpenGL and SDL 2.0, Gabe Newell personally promoting their Linux activities to other game studios and developers, Valve ensuring their own titles reach Linux and are of a first-rate status even titles more than a decade old, the mobile and home Steam gaming consoles running Linux that will greatly expand the number of Linux devices on the market, plus a lot more. The Source Engine coming to Linux directly led to significant driver improvements for Linux from AMD, Intel, and NVIDIA that benefit all desktop users too.
In terms of the original poster's other fears, NDAs are simply common in many B2B negotiations. From what I could infer from Gabe last year when talking about their original Linux plans, the cut that Valve takes from game developers distributing their titles on Steam is less than what Google takes from Android developers and what Apple takes from iOS applications. When it comes to their console plans, it's a much better bargain and easier to push down updates than what Microsoft charges for their XBox marketplace or Sony for their PlayStation.
Meanwhile, Desura coming to Linux really didn't do much and open-source gaming really hasn't advanced much at all. Most open-source games look like shit and beyond the artwork the latest open-source engines really aren't competitive or comparable to Source Engine, Unigine, or Unreal Engine 3. So while it would be nice if Source/Steam was open-source, it's not, but Valve is making great contributions to the Linux desktop.