> the bug does not need to be inside in unsafe block

The argument is that while you wouldn't in fact fix the bug by modifying the unsafe code block, the unsafe code block was wrong until you fixed the other code.

For example imagine if a hypothetical typo existed inside RawVec (the implementation details of Vec) causing the growable array to initially believe it has 1 element inside it, not 0 even though no space has been allocated and nothing was stored. That's safe code, and of course the correct fix would be to change it from 1 to 0, easy. But this broken type is arguably broken because the unsafe code would deference a pointer that isn't valid, trying to reach that non-existent value. It would be insane, perhaps even impossible, to modify that code to somehow handle the "We wrote 1 instead of 0" mistake, when you could instead fix the bug - but that is where the theoretical fault lies.