In order to get Steam working on Linux, one would probably have to make serious modifications to the Steam client, haxing the shit out of it, so to speak. This thougherly violates and breaks the terms of use agreement you sign when you install Steam, and thus is illegal and has no place on the Valve forums.
It takes absolutely no hacking or reverse engineering to get the steam client to function on Linux. All it takes is Wine, which is basically a Linux implementation of the DLL system used in Windows, that allows Windows programs to run in Linux natively. It doesn't use actual Windows DLLs however, can't unless you actually own Windows yourself, so the implementation isn't perfect.
To be clear, it takes no property from Microsoft of Valve, it's not an emulation of Windows, it's a compatibility interface. Anyway, using Wine, the Steam client will function well enough, as will some games, some of them very well. If you have a legally owned copy of windows, you can copy the dlls from that installation into the wine system32 folder and instruct wine to use native dlls. This adds a lot more compatibility and usually better performance, particularly if you manage to install DirectX on it.
So, no, unless there's a line in the EULA that explicitly states that it may only be installed on Windows for whatever reason, then claiming that it's wrong to use it on Linux is patently false.