I agree that the given evidence is weak, but I can still see that medical professionals believed that it's not pain that babies have. Maybe because it's not "proper" pain somehow, maybe because, circling back to the original argument, their consciousness is not there yet, so there might be pain but there's no suffering, maybe because they won't remember, therefore their experience is invalid. Desensitization is also an issue that happens over time - the mind has to cope somehow.

These are not facts and I respect that there's no hard evidence regarding these things, pro or contra. This is just how the world comes across to me.

The year 1999 comes from the second source in the sentence.