The world is harsh and unfair, so parenting should be as well?
The world is not always harsh and unfair. Humans live and work in groups, and this means much of the time we need to put the greater benefit to the group, above our own individual wants & even needs.
A school classroom is a good example. The teacher has 30 children to educate. If he/she has to spend all her time explaining to little Jaxon why he isn't allowed to get up and draw pictures of frogs on the white board while she's doing a phonics game, the other 29 children miss the phonics game.
Public transport is another. A pilot of a plane is responsible for transporting dozens of people. If they suddenly have an incident and issue an instruction to brace, people need to comply fast and without question.
A lot of this is about trusting people in authority to know better than you & make better decisions on your behalf, and it begins at home learning to accept and trust your parents to make decisions for you. Because as a young child, your parents know better than you 99% of the time. We learn at home that there are times its okay to question and challenge and times when we need to do as we're told.
Gentle parenting always seems to assume infinite resource - endless money, plenty of alternative toys/activities, infinite amount of the parent's time and attention. This simply isn't the reality.