Rachni: They shown up to that point to be monsters that only wanted war. The queen paints a different tale, sure, but that doesn't change how history remembers them up until that point. These were war beasts that denied any peace talks and only sought the destruction of our worlds. How terribly convenient now that this last remaining queen can say "oh but it wasn't our fault! demons did it! We innocent, swear!"
There's a reason why we hear the rachni's plea immediately after learning about the realities of indoctrination from Benezia.
It is, imho, one of the places where awarding P/R points doesn't make a lot of sense, because it assumes a motivation for the choice. Paragon = idealistic, Renegade = pragmatic - but this is one of those places where you can make a 'paragon' choice for purely pragmatic reasons. You mean I can have an entire species owe me their entire existence? A species that shares memories, and isn't going to forget that Shepard, a human, prevented their extinction? Yes, please.
The Reapers had a sudden justification in the end, too. Yet I'm willing to bet few care if Shepard grins or takes pleasure from completely wiping them out.
Ending the reaper threat was Shepard's #1 priority since ME1. Everything else was just a sidenote or in service to that goal.
Harbinger had harrassed Shepard endlessly, the reapers had killed not only billions in the current cycle, but many more in previous cycles. Shepard really ought to take great satisfaction in finally accomplishing that goal.
Terra Firma: So because a few nut jobs have extremist views any support for the party itself is inherently wrong? Someone should alert the republicans.
Aside from shunning greater involvement and integration into greater galactic society, what exactly did they stand for?
Shiala/Rana: Comparing either of these to Falera is unfair. Both Shiala and Rana were working for Saren, the enemy. Shiala may not had known what she was getting herself into but we are to just to accept her word that her actions were forced and against her will by some magical space ship. How convenient. We don't know about indoctrination at this point, this is the first we've heard of it. We just have to take it to her that the ship somehow controls peoples brains and that she is innocent. Foresight is 20-20, sure, but at the time I don't see killing her as being inherently wrong. Though I would had arrested her for her involvement instead - sadly that isn't an option.
What did Shiala do, exactly? She'd been somehow consumed by the thorian - and we saw the effects the thorian had on other colonists prior to meeting the original. The ones we fought in the thorian lair were clones. I'm not even sure she had been indoctrinated by Saren - she seemed completely free of that sort of influence once released from the thorian.
Neither of these cases are like Falera. Falera had committed no wrong nor was associated with any terrorist. Her only crime was that she was born with a genetic mutation. She is dangerous, yes, but killing her solely because she presents a possible threat is not the same as killing those who have actively committed horrible crimes already.
Agreed, especially after her solemn promise that she would not allow them to make her a banshee. Falere & Rila were obviously very close, and we witnessed Rila's sacrifice - I would expect Falere to do no less.