The point is that rewrites are costly and introduce new bugs. New software written in safe languages to replace old software will inevitably introduce new bugs

The point is that rewrites are costly and introduce new bugs. New software written in safe languages to replace old software will inevitably introduce new bugs and repeat old ones. That’s not a reason against using memory safe languages, but the danger is that a too-keen focus on memory safety risks devaluing other, far cheaper means of improving security. Yes, use memory-safe languages for new projects. But don’t lie to yourself and everyone else and say that they will come anywhere close to making a significant dent in the rate of security bugs.