3) I'd never work on life critical medical (or anything else) software, I know I fuck up and even the best can (and I'm not).
I simply wouldn't want it on my conscience that an easily preventable error (in hindsight) hurt someone.
For example, imagine you work in a bank on their mobile apps. You decide that implementing automatic bill payments for a certain type of account is too much technical effort and not worth it.
Hundreds of thousands of people with that account now have a subpar experience. They have to manually pay bills, and many will forget, leading to arrears, bankruptcy, payday loans, and prison.
Your decision not to implement that feature to make the lives of your customers better indirectly led to ruining the lives of tens or hundreds of people, who otherwise would have led a good life.
From an ethical point of view, unknowingly ruining a life due to an action or due to inaction, is pretty similar.