It remains a requirement, whether it is enforced or not.

Valid programs don't need guardrails, since you need to satisfy those requirements for the program to be valid in the first place.

Humans have a bad history of getting things right without the guardrails. We know how to do it, but there often is one code path we didn't think about correctly - we may get it right 99.99% of the time, but that leaves a lot of mistakes in the code.

I want guard rails to ensure that I got everything right, not just 99.99% of the cases right.