The dismissal of the importance of a rise in cortisol on the developing brain is very popular with extinction sleep training apologists. Although we do not know the exact influences, there are reasons to be cautious of this dismissal, which ignores key evolutionary and biological information.
Tantrums happen. Even to the best of us. The problem is when we feel our only options as parents are to ignore or give in. That isn't true. We need parents to know how to effectively handle tantrums for long-term emotional growth.