> Obviously in userspace it would only crash the running program and not the entire operating system? It's a significant difference.

Significant and often far worse. It would leave the machine running unprotected.

> It's a significant difference.

When various apps running the world are crashing, unable to execute because malware protection is failing, there is no difference.

_No_ difference oversells it, IMO -- the fact that the entire OS crashed is what made fixing the bug so arduous, since it required in-person intervention. To be sure, running the code in userspace would still cause unacceptable service interruptions, but the fix could be applied remotely.