Neither Hugs Nor Drugs

A 12 year old middle school student in Illinois was given detention for hugging a fellow student.
School policy states: "Displays of affection should not occur on the school campus at any time."
That's pretty clear, and we're sure this student was aware of it because she had previously been warned.
There are two questions here, was she treated fairly and does the rule make sense?
On the first there is no dispute. Similar to Pete Rose, she willingly broke a rule for which she knew the punishment. The fact that she got the punishment is perfectly just.
Does the rule make sense? That's a more difficult question. I can see why it exists, to avoid any interpretation to what constitutes a display of affection.
I think it would be hard to write a rule that could be enforced which allows hugging but bans other behaviors a school has a reasonable right to want to eliminate, such as kissing. If you specifically said kissing was banned kids could kids hug really close for a really long time while grinding their midsections?
While it sounds kind of silly I think the rule banning all displays of affection is probably a school's best option.