I think you are correct about his position. I just feel that it's not the right position for a library maintainer to take, especially the single most important library in the whole system.
The thing that bugs me is that there is a way to implement this change such that all newly-compiled apps get the improvement while older apps get the older behaviour. Sure, for Fedora that means that every single app which might have this bug is now vulnerable, but anything else will be fine. Lots of people have apps that they can't easily change. Many of those apps are even Free Software. Those users cannot reliably upgrade glibc, it seems.