Mass Effect 3 - Page 56

I think there was a misunderstanding for the Catalyst's voice. It may be that of the boy in the vent, but as we've no doubt seen many times, he dies. I think that it uses his voice in order to communicate with Shepard simply because he was really the first true death that Shepard witnessed during the Reaper's return, the first child and innocent to die, and that left an impression on Shepard that the Catalyst was able to use and communicate through.

So much wasted oppotunity in the reason for the reapers existance. Their entire reason for being makes no sense

Actually, from a certain point of view it does, but that reason also destroys the Mass Effect universe for any further use. With the mass relays destroyed, nothing will work anymore, and the galaxy will never be able to go back to pre-ME1 status because of it. It just wrecks the whole franchise, and I wanted something more optimistic. Even in the best ending, you are stranded from anyone else. I wanted to have the happily ever after ending, but apparently that was too much to expect.