> Why? One doesn't need to take a very strict view of what "robust and reliable extensible software system" means to conclude that we do not have such systems at the moment.

No. But we do have garbage collected languages, and we still don't have robust and reliable extensible software systems. So claiming that garbage collection is going to get us there does seem naïve.

But the original claim was that garbage collection is a prerequisite - not sufficient, but necessary. I still think that's naïve. But maybe, once we figure out how to do it, then we can figure out what language elements are necessary, and then we can see if garbage collection is on the list.

My bet: Garbage collection can help, but it's not essential.