That's stupid. In a series based on your past actions the game starts with you on trial for something you never chose to do?
That should be the opening.
It is a bit silly, more so because it was DLC that a number of people wouldn't have played, you also couldn't make any real decisions during the DLC, it happened regardless of what you did.
And yea, when they mentioned the trial due to the fallout of the Arrival DLC people expected to actually see a trial in ME3 as that is why you are back on Earth, but they are seemingly skipping over most of it.