The Silents are not the bad guys in this tale, they just keep history on track by nudging the 'little people' in the right direction to make sure all the fixed points still happen. Why they do this isn't important to us. The Doctor's death is a fixed point and must happen. That doesn't mean he doesn't have a signet ring though, a precedent for Time Lords returning from the pyre...
Whoa...now there's an idea. The Silence in the bathroom told Amy she MUST tell the Doctor...and the Doctor would presumably tell his friends NOT to alter the future. Although that wouldn't really explain why the Silence made that woman explode.
On a side note, when
the Silence killed that woman and said her name was Joy, I initially misunderstood since the dialogue went like this:
Amy: Why did you kill her?
Silence: JOY!!!
I thought he meant he killed her for joy, for the sheer fun of it. Did anyone else think that too? Or maybe it does fit...perhaps she was 'supposed' to die but for some timey-wimey reason, maybe Amy's presence in the past, she didn't, so the Silence killed her to make history accurate. That might explain why he told Amy what her name was, since if he was a pointless, monstrous evil monster he wouldn't care.
Amy: Why did you kill her?
Silence: JOY!!!
I thought he meant he killed her for joy, for the sheer fun of it. Did anyone else think that too? Or maybe it does fit...perhaps she was 'supposed' to die but for some timey-wimey reason, maybe Amy's presence in the past, she didn't, so the Silence killed her to make history accurate. That might explain why he told Amy what her name was, since if he was a pointless, monstrous evil monster he wouldn't care.