If someone attacks me as an adult, I have every right to defend myself. The police will be called, and if it's possible to identify the perpetrator and prove beyond a reasonable doubt that they attacked me, they will go to jail. If the police aren't able to find the attacker or prove that they did it, then I'm allowed to take countermeasures such as avoiding the area, carrying some sort of defensive measures (pepper spray, or even just a gun), or having someone escort me.
Do the same thing to a child, and there's often minimal punishment, the victim and perpetrator are not separated from each other in the long term, and the victim is strongly encouraged not to fight back.
Can you imagine telling a victim of a mugging (or worse) to "just ignore them" the next time it happens?
We create these Lord of the Flies type situations for children, then basically tell them that problems shouldn't be happening, if they are then we won't help, but the children shouldn't do anything about them either. And then we are shocked, shocked, when children suddenly go all psycho on their tormentors.
If a business had a constant known problem with physical violence among its employees and patrons, they'd be forced to reform or shut down, and people would go to prison. Schools should be the same. It's the responsibility of the people in charge to keep the students safe, both from outside threats and from each other. If they can't do that, then they need to be replaced by people who can.
Until and unless that ever happens, then students' best option will be to retaliate.