Did you read the link? Do you even bother reading the studies at all? Do you critically evaluate them in the least? Because every single study saying "there is no harm" fails to use any physiological marker as an indicator.
Every single one of them use
parent reported attachment, stress, and sleep quality as a measurement of harm.
Every study that says "there could be harm long term, there
is harm short term" uses either physiological measurements of stress or blind-reported independent evaluations of attachment and dyad interaction.
Everyone strawmans the extreme stress studies saying that they're not comparable to cio, but completely ignore the plethora of published work on mild-to-moderate levels of stress that also point to disimproved attachment, cognitive function, and stress management.
ETA: to bolded: Pro-cio-ers always say that baby only cries for a few nights. This completely ignores that it's been shown that
signalling stops,
stress does not. Just because they stop telling you about their stress doesn't mean it's not there. The other study based on mother-reported sleep difficulties also shows that sometime between 4w and 6mo after training has taken place, the infants made to cio and the infants with mothers who wio report comparable sleep reports-- meaning that either sleep would have sorted itself in that time or the cio babies stopped sleeping as 'well'. A majority of the cio families had had to sleep train again within the 6mo. So it's
not a few nights for most families. It's who knows how many nights of unsignaled stress, to be repeated
again when the training wears off.
ETA again: I have no interest in bashing the people, but I will bash the methods you may choose to use. Please don't confuse the two.