Final answer:
The letter's purpose is to support the Amish's right not to attend high school, citing the Wisconsin v. Yoder case as a precedent for religious freedom in education.
Step-by-step explanation:
The purpose of the letter to the editor, in response to a previous letter supporting the Amish's right to opt out of high school, is most closely aligned with supporting the right of the Amish not to attend high school. This stance is based on the significance of religious liberty and freedom as demonstrated in the Wisconsin v. Yoder case, where the Supreme Court found that requiring Amish children to stay in school past the eighth grade breached their religious rights. The letter seems to be using these historical precedents to persuade the audience about the importance of respecting the Amish community's educational decisions grounded in their religious beliefs, thus avoiding any excessive government entanglement with religious practice.