It's up to the player, if he/she wants to play an altruistic character that will help everyone, then the player will release Shadowheart Or the player could "RP" that the character doesn't know what the machine will do to Shadowheart, and thus leave her in. Alternatively leaving Shadowheart in the pod to die is something an evil character would do. But to respond to your first point: I don't think it's a problem that people free Shadowheart every time.
Your explanation for why the mindflayers leave Shadowheart in the pod with the gith weapon doesn't hold much water to me. It would be as simple as grabbing the artifact and placing it somewhere safe. And if an ilithid is indisposedm then have a thrall do it.
We both know the reasoning for why Larian did this: To few people doesn't use the tadpole powers. I personally liked the preavious iteration where they were a shortcut in order to obtain power, but felt like you did not get something substantial to tempt the player. That's why I am of the opinion that an ability score improvement and/or a feat for every milestone you reach in tadpole corruption is a better way to tempt the player. Not locking of Shadowheart away in the prologue to those of us that want to try a no tadpole run.
But then if you give stuff to the tempted player you create a problem where the one that dosent use it need to get something as well.. not to mention not everyone is gonna get "tempted" by extra stats (seriously feels like a lazy cope out to me) .. I definatly feel like there should be an alternative for getting her out of there.. but also I think its theyre way of introducing you to the tadpole because in reality a new player not gonna question "is this good or bad" Theyre just gonna do the option.. I know I have seen enough streamers clicking the "evil" options in games without even realising it was evil only for them to be all shocked and suprised and when someone died because of it.
