Also natural selection is much more biased against alkaloids (which are often found in plants similar to food) than against the sorts of sweet poisons like lead which is slow to kill and only widely present in very harmful doses thanks to refinement.
Some poisonous things are sweet, but a lot of natural poisons (and drugs) are bitter; alkaloids in general are bitter.
Also natural selection is much more biased against alkaloids (which are often found in plants similar to food) than against the sorts of sweet poisons like lead which is slow to kill and only widely present in very harmful doses thanks to refinement.