Why is the Chinese internet filled with arguments, insults, mockery, and personal attacks?

Because they were never treated gently when they were young. They were insulted, criticized, and subjected to violence by their parents as children.

As adults, they replicate their parents' behavior online, habitually denying others, and only find a sense of existence in arguing, criticizing, and negating others.

A child who was appreciated from a young age will also get used to appreciating others and the world around them.

So next time you see those who like to argue, insult, mock, or attack others, you should understand this: they had a very tough start in life, but they don't deserve sympathy; they are just living as they are.