ok let's talk about this link you quickly posted....
I quote directly from the second paragraph: "...medications, etc., are finding their way into the environment via human and animal excreta from disposal into the sewage systemラi.e., flushing unused medication down the toiletラand from landfill leachate that may impact groundwater supplies. Agricultural practices are a major source and 40 percent of antibiotics manufactured are fed to livestock as growth enhancers. Manure, containing traces of pharmaceuticals, is often spread on land as fertilizer from which it can leach into local streams and rivers. Conventional wastewater treatment isnメt effective to eliminate the majority of pharmaceutical compounds."
First point to be made is this is about dumping bottles of the stuff into the toilette not what naturally passes. I'm not saying that none passes. You can see from my previous lengthy post that even ibu comes through at about 33% so there is a load (now there is seriously no pun intended there) to be considered but when you consider most prescription drug dosages this becomes trivial in the grand scheme of things unless you happen to have a pack of geriatric hikers.
Secondly the last sentence I quoted proves my previous point about sewer treatment/CWA--it only handles solids not dissolved chemicals. Your prior assertion that the waste treatment process of sedimentation (removal of solids) would do the trick is...well just plain wrong by your own source. Sure some of the drugs go with the solids but the rest stay in solution and get dumped into the outfall of the treatment plant...untouched. And what does your sewer treatment plant do with it's filter cake? I can tell you from experience what most of them do...they send some to a lab to get analyzed via a procedure called TCLP (toxicity characterisitc leachate procedure) which covers 100 or so compounds--mostly pesticides, herbicides and petrochemical contaminants. Then if that passes they send it to a landfill. So by packing it out all you are doing is moving it from several small well dispersed sources to one very localized source that still does little to deal with the chemistry problem. It will however reduce the spread of Giardia et. al. but then again so will proper water treatment and proper water treatment will have a more immediate effect on a hiker than packing out his poo will: i.e. he won't get sick if he treats properly where as if he packs it out his pack jsut got heavier (too bad for him) and then there is the old out of sight out of mind thing working there too. It's an attitude problem with that portion of the argument and other than acknowledge it I wish to comment no further on it.
I'll answer your quesiton then you answer mine: The reason it is illegal to have an outhouse is simply population density. Think of the folks out in the country. They all have septic systems. Those bad boys treat for nothing---all they do is digest those solids again. I have no information on what the enzyme/bacterial action does to the prescriptions but I'd bet very good money that it's less effiecient than the minimal treatment that gets done at the local municipal plant. Furthermore those septic systems are typically 2 part systems a tank to digestion and a leach field. That leach field is where all the liquids go as the solids settle out in the tank and the tank usually has a gravel/open bottom so liquids that don't flow out to the leach field trickle down through the sludge and out the bottom. I'm sure you have heard the saying about where the grass is greenest--and I'm not talking about the other side.
With the permit to put a septic system in is the consideration of where the water sources are, percolation rates, drainages, rock formations and permeability. That is because of the massive quantity of stuff in the system and it's persistent presence. The septic system takes up a good chunk of land and because of this they can't have folks jsut doing it in the back yard. As you say if you go in your back yard everyday your yard will fillup very fast. I contend that your back yard is not, repeat not, a healthy ecosystem. It is for all intents and purposes a monoculture of some mutant strain of grass and then you figure in all the chemistry that goes into keeping it that way. You have no flora/fauna to handle said deposits. Look at when your dog craps in your back yeard as opposed to on the side of the trail.The stuff along the trail lasts very little time because there are organisms in that ecosystem that deal with that sort of thing. Otherwise crap would be knee deep just from the deer and bear right?
So given that by your own source the chemical load is not leaving the waterways via sewer treatment what is to be gained by packing it out other than the potential of bacterial contamination which is easily enough handled by proper treatment. I will conceed that it may reduce waterborne illness but so will water treatment.
Now my question that you didn't answer--at least that I saw: What do you do with your big bag--the dry bag you packed all the poo in? Are they reusable or does the system you are advocating make them one time only devices? By one time I mean one mass dumping not each movement. You certainly can't carry them with you on any public transportation...that is a violation of a whole basket of health and DOT codes. So throw me a bone and tell me how many cycles (fill/empty) do you get out of a single bag?