What I implied by "programmers are human" as exactly that they are 1x and make mistakes. The tools help in the situations where "100%" assumptions cannot be made. But you can't put a seat belt on everything and contain every issue because it will cost more.

But you must also know that you must trust at least part of the environment your operating in. There will never be a language or a tool that can make a program useful and correct when nothing can be trusted. C/C++ regarding UB is just explicit about trusting the code that is currently being compiled for the sake of optimizing code that actually is. I get where you're coming from, but this is one of the possible solutions, and a very widely accepted one given that the whole world runs on C.

Managed languages might avoid some class of bugs, but they will always retain some, and I'm not sure it is possible to guard against all without solving the halting problem. Some C/C++ people might on the contrary find it bizarre that your languages do absolutely unnecessary bounds checks. None of them are better than the other on an absolute scale, it all depends on what you want to use the tool for.