Not who you're replying to but I've spent a lot of time reading about this particular aspect of law. I more or less happen to agree with you, but this is one of those examples where I think we've taken a lot of small steps in one direction and all of a sudden it looks crazy to an outside observer who doesn't understand the full context.

There's a concept of you "altering" your lunch such that it becomes dangerous or inedible but still leaving it out, e.g. in a fridge, where a reasonable person would assume that the lunch is edible. If you put rat poison in your lunch then throw it in the garbage, it's going to be harder to argue that you intentionally hurt that person who stole it. Even harder is if you put in a biohazard disposal bag.

There's the concept of the severity of the offense - poisoning someone is worse than stealing their lunch. Nobody is calling the cops because their lunch got stolen once.

There's intent. If you poison your lunch and put it back in the fridge, you're accepting there's a chance someone takes it. Can you prove someone intentionally took your lunch as opposed to accidentally taking it? You can accidentally take the wrong takeout container, even multiple times. You can't accidentally poison your own food.