Good. The path to evil should be easier and more immediately rewarding. Otherwise, no one but sadists and/or idiots would choose evil.
Not too sure that our characters (as players we know too much) would consider the use of the tadpole at this point as being rewarding, we know nothing about what it will do to us. I think that the type of characters (usually good aligned) who want to save anyone in distress would be more tempted to use it here. An evil type may not see the risk as worth it because self preservation is more important than saving some random person. If they added something about us sensing some great power coming from inside her pod then it might tempt the more traditional evil types to save her because it might actually be worth the risk.
That's fair. This example falls into the "tempting a good character to become evil" situation (which is great!) but wouldn't necessarily be appealing to an already-evil person. Although it *could* be appealing to a self-interested person->saving SH puts her in your debt, and henchpeople are always useful. Can we sense that SH also has a tadpole while she's still in the tank, and that there's a connection between us? That by itself might be a good enough motivation for an evil character to free her...or to leave her trapped. :P
As to the claim "we know nothing about what [the tadpole] will do to us": Our characters, living in the Forgotten Realms, almost certainly know that mind-flayers are evil and listening to a magic voice in your head that suddenly gives you power is probably bad. So if they're at all intelligent, they can probably reason that using the tadpole *might* have drawbacks, and then have to decide if that risk is worth saving SH.
