@Hardbackwriter managed to respond before I returned to the thread but I will share some actual evidence based info below for OP and others reading to clear some things up. It’s a myth that sleep training is harmful. Not everyone has to sleep train their baby but it IS harmful to spread misinformation about how bad it is.
Also quite horrified that people are suggesting unsafe sleep practices such as bedsharing as an alternative to a safe, well researched sleep training technique, but sadly not surprised.
I don’t expect posters who’ve already decided sleep training is damaging to bother educating themselves but others might find it helpful :) If anyone wants a good starting point for themselves to investigate the evidence around sleep training there’s an excellent, non biased and evidence based chapter in the book Cribsheet by Oster which is great, looks at all of the relevant major studies and examines the results and their applicability, for example the Middlemiss study is often cited as ‘proof’ ST is harmful but it’s been thoroughly debunked, the information that came from that study was unusable due to their methods.
No peer-reviewed research has reported detrimental effects from sleep training.
pediatrics.aappublications.org/content/130/4/643
pediatrics.aappublications.org/content/early/2016/05/21/peds.2015-1486
pediatrics.aappublications.org/content/122/3/e621
pediatrics.aappublications.org/content/111/3/e203
Here's a look at the Middlemiss study, which is usually cited by people against sleep training or extinction (CIO): expectingscience.com/2016/04/21/the-middlemiss-study-tells-us-nothing-about-sleep-training-cry-it-out-or-infant-stress/
And here are the authors of some of the studies on child abuse and neglect say that anti-sleep-training people are mis-citing their work: ideas.time.com/2012/05/10/the-science-behind-dr-sears-does-it-stand-up/
A little information on the "cortisol" fear.
"In terms of their effects, the difference between short-term and chronic stress is one not of degree, but of kind. Short-term stress enhances memory; chronic stress impairs it. Short-term stress boosts the immune system; chronic stress weakens it.
So where does that leave us? A little stress, even in infancy, is fine, if not beneficial, but too much for too long is very, very bad.
Do we know exactly where sleep training fits in this spectrum? Just how much stress does a baby experience during cry-it-out?
The short answer is that we don’t know for certain. Everything we do know, however, suggests that this amount of stress, in the context of a warm, loving family, is just fine.
Sleep training is not only not harmful, it is beneficial. Successful sleep training can decrease depression and chronic stress in the parents, and this benefits parents and their babies. Unlike sleep training, having a depressed mother during early childhood has been shown, repeatedly, to be linked with worse long-term outcomes for children."
expectingscience.com/2016/04/12/critics-of-cry-it-out-fundamentally-misunderstand-how-stress-affects-the-brain/
" To measure the effects on the babies, the researchers did something interesting: they measured the level of cortisol, a stress hormone, in the babies’ saliva. They also asked the mothers about their levels of stress. Twelve months later, they looked for any emotional or behavioral problems in the babies, and they also did testing to see how attached the babies were to their mothers.
Here’s what they found. The babies in the graduated extinction group and the bedtime fading group both fell asleep faster and had less stress than the control group — and not only that, their mothers were less stressed than the control group mothers. Of the three groups, the extinction group babies were less likely to wake up again during the night. And when it came to emotional or behavioral problems, or attachment, all three groups were the same.
This means that it’s okay to let your baby cry a little. It’s not only okay, it may lead to more sleep all around. Which makes everyone happier."
www.health.harvard.edu/blog/new-study-says-okay-let-babies-cry-night-201605319774