If you want to abuse then there are already hundreds of ways to do that I think.
If I want to make script that will rewrite/unload existing scripts I could choose similar approach I described earlier (Looping through existing scripts and then unloading/tampering with them). That doesn't mean that /unload command should be removed simply because some scripts could use it to unload other scripts.
Its definitely possible that some people will start abusing such event. However if we would take out all commands/events that can be used "wrong way" there wont be much left.