UB has [developed a lot][1] since then. Now UB is a way for the programmer to help the compiler generate better code by providing extra information that is hard for the compiler to prove itself. I think, in general, this is actually an ingenious idea (I have [written about this][2] in the context of Rust before). But it can surely be taken too far, and it is particularly a problem when the programmer is not aware of the promises they are making. This is more an API design problem though than a fundamental problem with UB itself.

[1]: https://raphlinus.github.io/programming/rust/2018/08/17/unde...

[2]: https://www.ralfj.de/blog/2017/07/14/undefined-behavior.html