Chopping off all the students heads because they might otherwise do poorly on tests is
also a straightforward policy. That doesn't make it a good police, and I fail to see why being straightforward is remotely relevant.
You're saying that someone defending this kid on the grounds that a stungun is ok simply because he might have brought a gun is the same as me saying that weapons of all kinds are dangerous, too dangerous to bring to a school?
Yes. The argument is exactly the same. "It could have been worse". That you manage to come to exactly opposite conclusions just exemplifies how terrible an argument it is, really. It's no better an argument for "we must always punish as if it were as bad as the worst case scenario" than it is for "we shouldn't punish the kid at all".
This isn't to say I think policies against weapons are bad. I also don't think this situation would deserve the full brunt or impact of such policies.
That example/analogy has absolutely nothing to with this situation. Even as an example it doesn't make sense, but there's no reason to get in to that.
Let me try a different one then. Putting someone in a bad situation where most people would respond poorly, and then acting like a dick to them when they respond poorly is not acceptable. Sometimes, like in this case, responding poorly is not acceptable either! By no means am I absolving the kid of blame. But that doesn't mean the person who trapped in in the situation gets off scott free - the school is equally liable for the expulsion, because it allowed things to escalate to that point.
Letting the school off for the expulsion, forget the bullying, is very literally saying that being a victim is a students only option.