Torrible wrote...
The fact is, they join you for a certain cause. They understand that sacrifice may be necessary. But for them to be sacrificed in that manner when there is a much better option (from their perspective) that achieves the same aim (ending the Reaper threat), I think a huge part of that implicit contract is broken.
Okay, at risk of derailing the thread...
ONLY IF there is a one hundred percent guarantee that the other options are indeed better, and that they do end the Reaper threat. Most people here pick destroy because it is the only ending to 100 percent end the threat by removing the Reapers (we know from metagaming that they do, but if it were a real scenario, you could not confirm this).
That's the problem with fighting a "war" from a troop standpoint. Sometimes your commader will have to make the decision
they feel will be the most beneficial - be that sacrifice or not (and we trust them to do so, because they have the experience and training necessary to make such decisions). That is part of the consent of being led into battle. If at any time you would question your commanders ability to make that decision (to sacrifice you) for any reason, then you probably shouldn't be fighting for them in the first place.
To tie this back into the OP (Yay, I didn't have to derail the topic!), the reason why most people feel this is a betrayal is that EDi and the Geth weren't given any sort of warning that they would be sacrficed, either by means of issuing an order, or at least Shepard being able to attempt an apology for choosing to destroy all synthetic life. It would have been nice to acknowledge this feeling within the game (such as it was for the Batarian Colony of Aratoht, where a Paragon Shepard had the ability to warn them of the Relay's destruction). If the destruction of ALL synthetics was really necessary for the writers' "vision" of the ending, it would have been a nice touch to see EDI accepting Shepard's apology, or like another user said, to watch a cutscene of the Geth hearing the warning, and then choosing to fight to the end.