The code in those libraries has been run billions upon billions of times, by billions of people. Sure, the libraries are written in unsafe languages, but they are incredibly battle-tested. Depending on your perspective, this may or may not be as good as a formal guarantee of correctness; at the very least there is a strong probabilistic argument for their correctness and safety.
The 1% of code that is your own will, upon creation, have been run precisely zero times, so there is no probabilistic argument to be made for its correctness. Safe languages let you exclude entire categories of mistakes even when your code hasn't been run yet, which seems obviously valuable.
The 1% of code that is your own will, upon creation, have been run precisely zero times, so there is no probabilistic argument to be made for its correctness. Safe languages let you exclude entire categories of mistakes even when your code hasn't been run yet, which seems obviously valuable.