If needed, all we need to do is turn to India to understand the difficulties of unrestrained fecal matter. They have been addressing this problem for several years as they've gained enough economic strength to develop infrastructure, education, and implementation of assorted human sewage systems.
But, in turning to even the pet dog.... In an increasing number of communities there are codes about the proper placement and handling of dog fecal matter. Many codes include the back yard, land-mine, variety of dog fecal matter. One of the very serious issues related to the placement and handling of dog fecal matter revolves around disease; parvo can hang around in the soil for at least 7 years as a potential infectant for other unvacinated dogs. Some dog diseases can affect other species as well. Another very real health threat for all critters, from dogs to humans, is the spread of intestinal worms as well as a number of different nasty bacterias.
The Texas AG's argument could easily be applied to something like methane gas. Courtesy of Oprah, Dr OZ has told us that the "normal", "healthy" human releases/has eruptions of methane gas several times per day. Yet, we welcome regulation of methane gas concentrations both for our olfactory sensibilities and for our safety in the case of landfills, underground fires, and explosions. As with many things relating to the environment, methane release into the atmosphere is not purely an on-off, black-white, or zero tollerance policy type of thing.
Rather, it takes some common sense to be able to make a rational decision. The same goes with CO2 production and release into the atmosphere. The carbon credit and carbon neutral types could probably tell you how to calculate how many human respirations are equivalent to a vehicle's output of CO2. But, common sense would tell us that the human produces considerably less than a vehicle per hour of operation, a vehicle less than most factories per hour of operation, and so on; also, which of the three can operate more sustainably..