How do you sanitize? Thats the whole point. How do you tell the difference between instructions that are good and bad? In this example, they are "checking the connectivity" how is that obviously bad?
With SQL, you can say "user data should NEVER execute SQL" With LLMs ("agents" more specifically), you have to say "some user data should be ignored" But there is billions and billions of possiblities of what that "some" could be.
It's not possible to encode all the posibilites and the llms aren't good enough to catch it all. Maybe someday they will be and maybe they won't.