Lexington, Mass. — David and Tonia Parker are asking their neighbors in this liberal town for one consideration: Tolerance. The Parkers believe homosexuality is immoral. So they were appalled when their son brought a picture book home from kindergarten that showed families with same-sex parents. To ensure his "spiritual safety," they demanded the right to pull him out of class whenever homosexuality was discussed. To deny them that right, they say, would be intolerant of their faith. School administrators offer a different take on tolerance. They say it's their job to expose children to the world's diversity. Supt. Paul B....