That all makes a great deal of sense. Nice one.Pretty much.
The idea i've constructed is that the Silence are a shadowy organisation dedicated to making sure that no one ever gets access to the Doctor's tomb, which would essentially give anyone villainous the potential to erase the doctor's deeds and destroy the universe. Like they say, "silence would fall", as all life could be wiped out if the rip in time that is the Doctor's body was misused.
Therefore the only way to stop the destruction of the universe in their eyes is to kill the only man who can open the tomb, the Doctor himself. The Doctor's name opens the tomb, hence the saying "Silence will fall when the question is asked. Doctor who?" if he speaks his name and opens the tomb the universe could potentially end.
The Silence made three assassination attempts on the Doctor. The first was by blowing up the TARDIS, ( the explosion resulted in cracks throughout time), however the Doctor averted this. The second was to train the part-time lord daughter of Amy and Rory into a psychopathic killer, who was raised to kill the Doctor, this once again failed, and River Song broke free of the Silence's control. Their final attempt on his life involved trapping the older River in a space suit, and sending her to kill the Doctor. The Silence believed that they succeeded with this plan, but they were fooled by the Doctor, who led them to believe he had died.
So in a twisted way the Silence are almost heroic, they want to unsure the safety of the universe, but believe the only way to do so is to kill the Doctor, therefore preventing his tomb from ever being opened.