What culpability do her parents have?
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Part of her complaint is that the school failed to protect her from the ridicule of other students. I know people who refused to put Obama or Romney bumper stickers on their car because the election was so contentious, yet these parents had no issues sending their child to school in a Romney shirt.
Did they assume everyone at the school, all the students, were Romney supporters?
Not even an issue. Why should anyone operate under the assumption that their child would be attacked and bullied, particularly by a
teacher, or not afforded adequate and appropriate protection from such bullying by other students by school authorities. What you are proposing is just like blaming the woman who got raped because she was wearing a short skirt. She should have known better than to wear a short skirt, or show too much cleavage, because that just incites men to rape.