Why should unconditional love for children be practiced?

Because the lives of ordinary people have little room for upward mobility. You are bound to be a slave in this life; moving from a small city to a big city is just moving from a pigeonhole in a small city to a pigeonhole in a big city. Even studying abroad is just serving foreign capitalists as a slave. 99.99% of ordinary people are like this.
You push your child to depression, push them to jump off a building, and in the end, they still become a slave under a capitalist, just in a different form.
And your child, as the person who loves you most in the world and the only one who might have unconditional love for you, if you treat them this way, not only do you fail to accept their love, but you also drain their emotions endlessly. Without a doubt, you will lose the only person who might have loved you.
Why are foreign parents so relaxed and loving towards their children, without harsh education? Because the people in developed capitalist countries have been baptized by capitalism for hundreds of years. A thousand-year turtle, ten-thousand-year turtle—they are very clear about the fate of ordinary people in this capitalist society. The love ordinary people can get, besides loving themselves, is family love. For ordinary people, there is no chance for class mobility. Striving and involution only make capitalists richer, and you will only become Gao Guanghui.
This game has been played for hundreds of years in several versions, and you are only playing for the first time. It's normal not to understand it.
Many parents in China are not actually anti-social personalities; they just haven't figured out how to play this game. Because they are stupid, so they are bad.