Here' the flamewar money quote:

(in reference to the pain of using multiple languages on a project) "At Meta we have a lot of projects that use React frameworks, you've got javascript here, and then you have C++ for real work, and you may have Java interfacing with some other part of the Android system, and those are all kinda horrible things."

Of course just a few minutes later Carmack says that garbage collection is unequivocally a good thing for most programs, so C++ pros shouldn't puff up their chests too much!