I will be the first to admit that I look at people keeping fish- not to make them uncomfortable, but to make sure the fish are not in the slot. Just yesterday (Sunday) I noticed a fella spin fishing successfully, and immediately putting each caught fish on a stringer (he was at the rebar hole). After hearing him ask his buddy if the fish he had just caught was a rainbow or a brown, I looked at the stringer I also noticed a jar of salmon eggs (yeah, I know), so I approached him. I told him, in an obviously hushed and non-antagonistic voice, that what he was doing was very illegal. It turned out that he had just purchased his MO license and was completely unaware of the regs... he didn't even have a ruler of any kind. I loaned him mine, he measured then released the fish and was grateful to me for letting him know. (Anecdotal, I know, but relevant.) Personally, I am fine with people keeping <12'' fish, but there is nothing wrong with tactful enforcement of the regulations... even if doing so makes some folks a little uncomfortable.
I am surprized no one has discussed the supply/demand aspects of Taney's ecology and how that relates to keeping fish. The rule of thumb for trophic structures is base 10. That is, the total biomass of aquatic insects, scuds, sowbugs, etc (everything that these trout eat) has to be 10 times greater than the biomass of the trout in order for the population to be sustained. (Likewise, there has to be enough of the right kinds of periphyton and algae to sustain the "trout food" populations.) So, the best I can figure is something like this: by not keeping fish, the demand for "trout food" remains high and distributed over a wide range of trout sizes. Basically, all the fish have to compete for all the food. From this perspective, having a lot of fish will make it harder for any single fish to acquire enough resources to reach trophy size. On the other hand, I am a long way from being convinced that the big (15lbs+) fish in taney got that way without a hardy amount of fish guts in their diet.
I don't know a lot, and I am aware that Taney's ecology is probably far more complicated than that, but I think it is important to realize that MDC understands Taney's ecology (hopefully) and that the management methods depend on a "put and take" system.