I think the works of Dr. Benjamin Spock had a great influence and lasting legacy in this regard, but not in the same way many of his critics claim.
His revolutionary concepts in raising children sold hundreds of thousands of books in the first couple of decades, and several millions of copies by the mid-1990s.
The problem? Many people who read his books implemented the easy stuff, modified the more challenging stuff, and disregarded the difficult stuff. And, of course, some of it was just off-base.
He taught that parents should rely more on instinct, should show more affection to children, should discipline rather than punish, and should be firm and consistent.
Too many people took that to mean that they should disregard whatever the pediatrician told them about general age guidelines (easy), show more affection (easy), set a few guidelines (not so easy), be best buddies rather than parents (bad and ineffective), and never punish or discipline.
Several generations later, too many children are being taught that they set the rules, there are no consequences, and you are never responsible for your own actions. That's a recipe for disaster, complete with sidebars and illustrations.