In the episode "The Wedding of River Song" we see the Teselecta, resembling The Doctor, being shot by River Song wearing the astronaut suit. The community, to justify the messing with a fixed point in time, agrees on the fact that's how the things should always had to go and The Doctor never meant to die at Lake Silencio.
Point is, and that's always bugged me, why the universe tears apart when River fails to incapacitate the Teselecta? I mean, even assuming that the robot was so important (and I fail to see why, considering what it is meant to do) to be a fixed point, it's just a robot. People are giving it purpose, they could rebuild another one, not even similar, and there will not be any change in history. It's like the most important toaster in the world.
How could that ever be a fixed point in time and space?