Awexsome said:
However the tiny things start to add up. First there's plotholes that would be explained (or rather, eliminated since they didn't really happen) like EDI possibly surviving the destruction ending which is supposed to kill all synthetics and how the Normandy got into a mass relay so damn fast with crew members that were on the planet.
But how do we actually know that the destroy option really does destroy all synthetics? The game doesn't show that happening. The only evidence is that the Catalyst says so - but how do we know the Catalyst is telling the truth?
The Catalyst wants you to pick "Synthesis", because that's the only outcome where the reapers survive in any meaningful way - both "Destroy" and "Control" wind up obliterating the reaper's minds, either by destroying them outright or overwriting them with Shepard's. This is why the Catalyst claims that Destroy will also kill EDI and the Geth, and shows you the Illusive Man grabbing the levers when talking about the control option.
Then there's the hints like the "catalyst" kid try to subtly lean Shepherd towards the Synthesis or Control endings which would spare the Reapers or the ending showing Shepherd taking the breath ONLY in the high war-asset destruction ending.
Here's my take on it: the "conduit" we see in London isn't actually a conduit at all, and doesn't really transport you to the Citadel - my evidence being that mass relay transit tunnels are blue and purple, not bright white like the beam coming from the "conduit". In fact, the "conduit" in London is actually a Catalyst interface device.
In the final charge on the conduit, Shepard is critically injured by the reaper beam, and the physical trauma has put him into a shock-like state, but he still managed to get close enough to the "conduit" to mentally interface with the Catalyst.
Shepard's brain, already overwhelmed by the damage he's taken, nevertheless tries to make sense of what's happening. Everything that happens on a citadel is a hallucination - Shepard is actually still unconscious and dying in London, but his mind is nevertheless communicating with the Catalyst.
The final action Shepard takes is actually a visual metaphor concocted by Shepard's dying brain - thus for example "Control" shows Shepard grabbing a set of control levers even though that's a completely illogical means of controlling a fleet of sentient starships - but the choice is nevertheless very real.
What I say really happens is:
Destroy - Shepard mentally directs the Catalyst and Crucible to issue "self-destruct" commands to the entire reaper fleet.
Control - Shepard assumes direct control over the entire reaper fleet, overwriting their own code with his consciousness.
Synthesis - Shepard transmits his consciousness around the entire reaper fleet, bearing code updates that make them realize that their entire belief system is wrong.
Thus, "Destroy" is the only ending that Shepard can survive, because it's the only one where his consciousness doesn't leave his body.
(More background information on my interpretation of events can be found in
this post.)