User blog:LDR/Cerberus gone mad?

I understand that Mass Effect 3's story isn't fully revealed yet, but why would Cerberus be out to kill Shepard? The Illusive Man wasted billions of credits to revive Shepard, so why would he kill the Commander now? Also, even if the Commander didn't tell the Illusive Man to "*bleep* off" at the end of the game, and if Shepard gave them the Collector Base, why would they be out to kill Shepard? It just makes no sense to me, and maybe someone could clear this up. Also, if Cerberus kills Shepard, how will they be able to combat the Reapers?