I really told myself I was gonna stay out of this, but...
In spite of some people's well-intentioned thought to put in more toilets, I think the idea is to take out toilets in some of the areas with the most problems. No matter how much you try to educate people to not throw trash into the composing toilets, people do it. Because there are no trash cans in the canyon, it is very tempting for some, and I have seen people do it. So people will find a way to abuse the system, no matter what that system is. For the park, abusing a system of composting toilets is no doubt extremely expensive. Removing some of the toilets will be (they hope) cheaper. Even though I'm sure some will throw their "wag bags" in the composting toilets, it's not as if the program will start a new problem, since people are already throwing trash in the toilets.
The other aspect is trying to help clean up the areas that never had toilets. Spending a lot of time with newbies in the desert is part of my job, and I can tell you everyone picks the same spots to poop. It is almost funny to see the look of surprise that someone else would have ever found "their" perfect spot. Humans are creatures of habit. Large areas pockmarked with catholes can develop, creating quite a stink near campsites, not to mention unsanitary. There are a few things to be done - encourage people to carry out their feces or make the rangers do pooper scooper duty. Would you want to pick up other people's feces? The rangers had to do dreaded seasonal cleanups through Buckskin Gulch until they instituted a pack-out regulation.
btw, those bags have a mixture of chemicals and microbes in them that are activated when wet. It actually does a pretty good job of breaking things down. At that point, the contents are OK to put in with normal garbage, whereas raw feces are not.
To me, this is a minor inconvenience that climbers and those packing in the arctic have already been doing for some time. Well, that was way more than

I'm afraid.