At my house, we've largely given up on growing "greens" because there are so many edible and tasty weeds that come up all on their own without any help. Our mainstays are chickweed, broad-leaf plantain, violet, dandelion, and lamb's quarters but there are a ton of others (amaranth, galinsoga, dock, burdock...) -- and it's worth noting that many of these were actually brought over by European colonists or were cultivated by Native Americans. They're just thought of as weeds today, but they make a fine salad.
Many of these would be bad to eat in large amounts, but humans are "generalists" -- we're built to eat smaller amounts of a variety of things together. The same is true for a number of our modern cultivated crops; off the top of my head the things in the mustard, spinach, and carrot families are mildly toxic, but we eat moderate amounts of each, so it works out.
This entire article could have talked about only oxalic acid and it would be a better article. It’s basically what all plants have to make themselves largely inedible and it the most common toxin in plants. You can eat all of the above but oxalic acid is just not good for you even small quantities. We’ve managed to get oxalic acid out of everything we’ve domesticated.
"deal with kidney stones down the line" isn't compatible with "not good for you even small quantities"
Some of those vegetables are staples in vegetarian cuisines like here in India. There would have to be a huge epidemic of kidney stones if the latter claim was true.
You're correct that many of those things have a lot of oxalic acid, but that domestication often reduces it -- but quite a few of our domesticated crops still have a large amount. We haven't gotten rid of it! The spinach, brassica, and carrot families are high in oxalic acid and/or oxalates, as are a bunch of fruits. And rhubarb is absolutely loaded with it, of course. All things to avoid if you have a family or personal history of kidney stones...
The other big toxins that come to mind are cyanogenic glycosides, lectins (improperly cooked kidney beans can kill!), and phytic acid. Those are well represented across a huge number of domesticated crops. But again, we use cooking and/or moderated consumption to deal with it.
Many of these would be bad to eat in large amounts, but humans are "generalists" -- we're built to eat smaller amounts of a variety of things together. The same is true for a number of our modern cultivated crops; off the top of my head the things in the mustard, spinach, and carrot families are mildly toxic, but we eat moderate amounts of each, so it works out.