Why does the older generation resent the younger one?

It's so typical to hear they hate that they had to do a thing in their day and don't want their own children to have the freedom not to do those things now that they're no longer necessary.
Had a father complaining about his daughter being vegetarian, his response "Well I had to so she should have to as well". You didn't like being controlled by your parents so you choose to inflict the same control over your own. You'd think it would be the last thing any empathetic parent would do to their child.