I agree that Round-Up is not very toxic to humans and not highly carcinogenic, in occasional exposure. The main concern about Round-Up for humans is for farm workers who have frequent exposures to higher doses of it and to inhalation (note most of the studies of RU carcinogenicity test oral exposure, but it is broken down in the digestive system, inhaling it is much more toxic). RU is now being linked to increased rates of cancers and birth defects in farm communities.
BUT my main concern about RU is not about humans but about its effects in the environment. Glyphosate can be acutely toxic to non-target plants, including aquatic plants and algae. The effects of this toxicity on natural plant succession alters the ecology of treated areas. In most cases, the plant species diversity will decrease, and along with it, the numbers of insects, mammals and birds utilizing these areas as habitat.
Glyphosate does reduce the growth of beneficial soil-dwelling mycorrhizal fungi, which function to increase nutrient uptake by plants through a symbiotic association with the roots. Mycorrhizae have been implicated in the improved resistance to stress, and are necessary for the proper growth and development of most vascular plants. Glyphosate destroys nitrogen-fixing bacteria in the soil. Glyphosate, by inhibiting the growth of some microbes, allows the overgrowth of others. This includes microbial plant pathogens. Fusarium is a naturally occurring soil fungus that is a plant pathogen. Fusarium invades the roots of plants and either kills the plant outright or prevents normal growth. Thus plants in areas treated with glyphosate will be more vulnerable to fusarium and other pathogens.
This is a thread I did collecting a lot of data about various herbicides and pesticides used in the garden: https://www.helpfulgardener.com/forum/vi ... 11&t=57653
It gives a lot of the citations where this info comes from.
So if you aren't going to use poisons, then what? Part of my answer to that is not to try to have a grass monoculture, which is a barren wasteland as far as any ecological value anyway. One of the commonest lawn weeds is clover, which is a nitrogen fixer and good for your lawn and it has nectar flowers that honeybees love. Dandelions and violets provide lovely bursts of yellow and purple color and are edible. Dandelion has a deep tap root, so it brings up minerals and nutrients from deep below the surface. Very beneficial in the compost pile, where these are released. Plantain is another common lawn weed and it is a wonderful healing herb, which takes the pain right out of bee stings. So I am happy to let my lawn be a miniature meadow. As long as you keep it mowed, it looks just as smooth and green as anyone else's lawn.
What I do is just dig out weeds that are large, coarse like thistles, etc. Whenever I dig a weed out, I immediately plant grass seed in that spot. In this way, I keep the lawn being partly grass. If in some spots, the ratio of weeds to grass is getting high enough that it isn't looking as much like a lawn any more, I give that patch a good hard raking, to get rid of thatch and expose more dirt and then over-seed with grass seed.