@Shitandhills I recommend the Emily Oster book as mentioned by PP. She quotes numerous studies suggesting that, as opposed to being harmful, cry it out and other sleep training methods actually beneficial for babies. Just one example:
"There are a number of good randomized trials that speak to this. One representative study from Sweden, published in 2004, took ninety-five families and randomized them into a sleep-training regime involving a form of “cry it out.”8 The authors focused on whether behavior during the day was impacted by the nighttime—basically, they asked whether the infants were less attached to their parents during the day as a result of being left to cry during the night. This particular study found that, in fact, infant security and attachment seemed to increase after the “cry it out” intervention. It also found improvements in daytime behavior and eating as reported by the babies’ parents. Note that this is the opposite of the concerns raised about “cry it out” methods.
Oster, Emily. Cribsheet (p. 178). Profile. Kindle Edition.
The data about attachment disorders comes from studies of children from Romanian orphanages, where children were seriously neglected, not from brief episodes of parents not responding in the context of a loving and nurturing relationship.
It's good news - sleep training does not harm babies! That must be good news to you, even if you have chosen not to do it! Of course we all make different choices and we just make the best decisions we can with the information we have at the time.