Without valid research in any direction, we should fall back on our prior, which is that ignoring crying infants at night is no less detrimental than ignoring crying during the day.
As I pointed out earlier in this very thread, the article itself mentions that there is no valid research on the long term effects of sleep training.
The only valid research says that they stop waking up their parents. This is probably due to learned helplessness, which leads us to the hypothesis in my first comment.