The authors of the study are scientists, not New Age/left wing rhetorists.

Chickens are birds, and process waste in a totally different way than humans, no matter what they eat.

The problem with cow farts is that yes, there are far more of them than when wild herds roamed the Earth. Also, they require quite a lot of space to raise, and since they are such a valuable commodity, more and more land is cleared each year to make room for them.

Because of this, they are a major cause of deforestation. Forests in and of themselves help stabilize the climate by consuming CO2, so finding alternatives to cattle farming is very important for all of us.

Part of the problem is that we give feedlot cows corn to eat, which is not their natural diet, and causes more enteric fermentation and methane emissions. Grassfed cattle, and wild bison, produce less methane, but also less beef per acre.

Finally, humanity has been consuming various species of insects for millions of years, and still does in many cultures. There is nothing wrong with insects as food, and in fact a lot more is right about them than many other sources. They can be raised in close conditions without psychological harm, reproduce at a much higher rate, and are a clean, tasty, healthy source of protein, essential fatty acids, vitamins, and minerals.