I think the problem is that some people do genuinely have a great childhood, or another phase of life (university is another one), while others have a terrible childhood or another phase of life, and people who have one fail to understand those who have the other.

To add to that I think people can have a rose-tinted view and deny what they felt at the time.

I miss the 70's when I was in high school. I had a great time. It's one reason why I drive a '72 Dodge. I feel like a kid in it every time.