Yeah, the original reasoning was that threads were something esoteric and
not used by most code, and at the time we definitely felt that always using
the GIL would cause a (tiny) slowdown and increase the risk of crashes due
to bugs in the GIL code. I'd be happy to learn that we no longer need to
worry about this and can just always initialize it.

(Note: I haven't read the entire thread, just the first and last message.)