Black-and-white thinking and argument is your enemy. Your use case may call for a lot of safety at the expense of performance, so you do run-time checks like th

Black-and-white thinking and argument is your enemy. Your use case may call for a lot of safety at the expense of performance, so you do run-time checks like this and sacrifice performance, or it may require extreme performance and you do static analysis instead of these wasteful run-time checks. There's no such thing as 'trust people'. If you write the code yourself you decide whether your own code is safe enough. If you are a manager, you look for unit tests, static analysis or do a detailed code review.