Ok, I guess I need to add some infos here
For what reason do you think Songbird pierced the black wall?
Not for her own sake that's for sure... Songbird did it because Myers order her to do it. In the same way as Myers ordered her to "betray" Reed years before (something that has haunted her ever since).
So why does she die?
Because she pierced the black wal, for Myers. So if someone risked the life of everyone on the planet by piercing the black wall, it's Myers and the NUSA, not Songbird.
Why she planned the whole shity crash?
Because for Myers and by consequences the NUSA, Songbird is a atomic bomb for them... She the living proof that by piercing the black wall, Myers and NUSA broke the international laws. Which can lead to another corpo war, but it would be the world vs NUSA. A war they sure will loose.
Myers keep a leach and a close look on her. Songbird don't have any other solution to get out, NUSA and Myers would never let her go (alive).
Either she keep doing what Myers order and die, either she try to escape, even with a shity plan...
Why did Songbird lie to V?
The same reason as V lied to Hanako. Hanako reveal you everything she know about Mikoshi because V agreed to help her... so except if you followed the Devil ending, V "lied" to Hanako too and at the end, she die because V didn't help her.
In my point of view, there are no reason to side with Myers/NUSA either
Yes, Songbird lied to V, Yes she killed people... But what do you think Myers will do if she get her hands on Songbird? She will simply stop what she did, she will become a "nice" president and will be respectful of the laws. No, she won't.... She specially asked to Reed to keep her head intact for a good reason... Continue her evil schemes and keep using the black wall as a weapon.
So again, nothing is full white or black here. But if you ask me and for what I gathered in the expansion, Songbird is the lesser evil compared to Myers/NUSA and by far
Hey, I never claimed that Songbird wasn't sympathetic or didn't have good reasons behind her actions. I only claimed that when V finds out the truth that from V'S POINT OF VIEW, there's no reason for him to still side with her and help her.
Every reason to still side with her comes down to Out Of Character knowledge and meta gaming. Or pure emotional sympathy.
Addressing your points one at a time.
So why does she die?
Be that as it may...we're not assigning who is most at fault here. Who, currently, is unexploded ordinance who might end the entire human race if she "blows" in the present? Song. I don't disagree with you on Myers' moral guilt. But, again, that's not the choice we're making. Disarming the bomb doesn't absolve the person who SET it no, but it's the most immediate, most pressing need.
Why she planned the whole shity crash?
Songbird's motivations are actually really well actualized in the writing. This part I have no objection to. WHY she acted this way is understandable...relatable...downright HUMAN. People want to live. But, I actually wasn't JUST referring to this. At the pivotal moment if you side with her and she does her thing...she causes hundreds, possibly thousands, more innocent deaths then and there too. You fight your way back through the marketplace that you've travelled any number of times before...filled with shopkeepers, hell...that damn robot that you manage to fix and reactivate for no reward.
But from a V perspective...what does it change? Again, Myers is morally culpable, but from V's perspective...is Songbird a good person? Is she worth laying down your life for?
She's lied to you and killed thousands of innocents to save herself. It is UNDERSTANDABLE...but...
You are LITERALLY one of the people she was willing to sacrifice to save herself.
Why did Songbird lie to V?
And again....so what? You can understand her motivations. but, once more, the argument to save her relies on meta gaming at this point....not V's point of view.
Myers is a total bitch sure. But, well, survival of the whole human race at stake basically trumps everything. Morally, the best arguments are either return Songbird and hope that NUSA has a vested interest in STAYING ALIVE and thus stabilizing her and preventing a full breech of the Blackwall...or killing her like she asks to end the threat.
Delivering her into some anonymous third party's hands with some sort of vague promise that it'll all turn out okay? Waaaaay down the list of rational choices.
She herself doesn't even know who arranged her flight, their motivations, their abilities, etc. Total blind leap of faith to hand a global WMD over.
Song is a one person global thermonuclear arsenal. If she goes off it is a global killer. The key is on the "person" part of it. She talks and has a mind and a personality. And that tugs at the heartstrings. Maybe she should never have been "made" to begin with, but you may as well argue against mankind having developed nuclear weapons. In a vacuum, yes, maybe we shouldn't have. The reality is that we did and it is better that they are in the hands of state actors with understood motivations than a complete wild card.
Do you want a nuke in the hands of a state government or some random ass terrorist cell that you know nothing about and can't predict?