> If you cannot have compile time guarantees on correctness, the discipline to not break things becomes a key feature. On the other hand, if you have strong correctness guarantees, you may more easily incur some breakage (and thus actually fix things).

Yes, and the result of that is cabal hell. Types aren't there to help you break your API. Once the API is out and it has users it is rude to break them. The linux kernel is a prime example how far can you get if you don't break your users.