The whole eating insects idea is motivated by carbon emissions and similar concerns: insect meal is around 60-70% protein (beans are around 30%, maybe bean meal is more but I have never seen it anywhere), and its cost in terms of emissions and land use is much smaller than either meat or plants (especially stuff like soy). Nobody is arguing that it should replace beans. Rather, it could help diminish meat consumption.
According to this study a mealworm farm uses more energy per kg of protein produced compared to chicken, but much less energy than any other meat. However, mealworm farms rank lowest in CO₂-equivalent emissions per kg of protein and lowest in land use compared to all meat products, including chicken.
Apparently soy beans produce 6.82 kg of CO₂-equivalent per kg of protein isolate (which is 90% protein, therefore 7,5 kg of CO₂-equivalent per kg of protein), while mealworm farms produce 14 kg of CO₂-equivalent per kg of protein (and around 30 kg for chicken, the next best option). Worse, but less than double.
As for land use, the first study calculates that to produce 1kg of protein from mealworms it is necessary to use 18 square meters of land per year (including the land to grow food for the worms) while according to this other study vegetable proteins need up to 25 square meters of land per year for each kg of protein.
I admit it's not as big a difference in land use as I thought (it's different studies, they might have slightly different metrics) , but I think there are other factors that make it a much more complicated issue: mass use of fertilizers, monocultures, deforestation, soil impoverishment... An advantage of mealworms might be that you can give them a variety of foods that are easier on the soil (the first study mentioned carrots, grains and other stuff) in order for them to produce protein, while protein-heavy plants require rich soil and tend to drain it fast.
The mix of possible food sources is something I hadn't considered. I can definitely see that insects could be useful for using up food scraps.
Land use is a complicated one. 18 instead of 25 m² is definitely something, but it pales in comparison to how much more land is used by cattle, pigs or chicken. And it's not like soybeans (or any other legumes) are intrinsically a destructive crop.
I agree, I honestly expected a much starker difference in land use. I also agree that soy beans can be grown responsibly, except of course it's often not the case. The fact that both soybeans and insects are being grown largely as a source of protein for cattle brings us once again back to the main issue: cows!
one minor nit to pick re: land use - not all land is created equal. you might be able to raise mealworms in places you can't raise chickens, which would alleviate food deserts and reduce the cost of getting enough protein to market in many places.