Final answer:
Keating tells the boys to rip out the textbook intro to encourage critical thinking and independent engagement with the material.
Step-by-step explanation:
The reason Keating tells the boys to rip out the textbook intro is to challenge their assumptions and make them uncomfortable. By removing the standard introduction, Keating wants to encourage the students to think critically and engage with the material in a deeper and more meaningful way. He believes that the textbook's traditional approach limits the students' potential for growth and independent thinking.