> So you aren't breaking any laws of physics, you are just able to make much better tactical decisions.

With respect I'd like to disagree on this subtly. A lot of games have the client send their cursor position at relatively frequent updates/packages (i.e. sub-second). So the server knows pretty precisely in which direction and to which object a player is looking.

This in turn can be readily used upon when using wall-hacks, as most players, who use wall-hacks tend to almost faithfully follow objects behind walls with their cursor, which good moderators can usually spot within a few seconds, when reviewing such footage (source: I was involved in recognizing Wall-Hacks in Minecraft, where players would replace textures, to easily find and mine diamonds underground).