Think about it.
Wheat is a seed. Basically, a type of grass seed.
And it does not benefit at all if it gets chewed up and digested. Not like some other seeds (fruit seeds) that use animals eating it to spread it around and boost the fertility.
But it does benefit wheat if it contains toxins or proteins that cause grief to anything that eats it.
If wheat grains wanted to get eaten, it wouldn’t be wheat.
It’d be a strawberry!
Peas do the same thing ~ over time we’ve developed toxin free varieties but down in the Sahel they still keep the old nasty ones that make you go blind ~ they plant them in the bad years because they’ll grow with little water. Then they eat them and go blind
You’re talking about natural selection. By that logic we shouldn’t eat chicken or steak because if you could see cows and chickens before they were domesticated, boy oh boy. Except we did domesticate them, as we did strawberries and wheat. And we made them better, or rather harnessed their evolution to our purposes. It just so happened that when we got really good at it we also got fat for unrelated reasons.