If poop was simply a thing dwarves produced from time to time as a result of eating, the mess of miasma or unhappy thoughts it would have caused would have been another obstacle the players would have had to contend with (and a realistic one at that, and I like realism) in order to keep their fort from having a tantrum spiral into oblivion. Truthfully, I would have found it very interesting to see how the players would have dealt with the problem. If they ended up making a poop trap (though how the hell enough poop could be collected for a practical trap given their often dire circumstances and how often dwarves would presumably poop is beyond me) to help combat the forces of darkness, then whatever; more power to them! They had a problem, they solved it! In that respect it wouldn't be gratuitous or immature, in my opinion. Use of poop and pee for any reason might be immature to some, but it is not without precedence in industry and warfare.
Poop and pee in warfare is not something only immature gamers think about (
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1305067/). An excerpt, if I may:
The use of biological agents was not limited to defensive or retrograde operations. Scythian archers in 400BC and Hannibal in 190 BC were probably the first to "weaponize" biological agents. The former did it by dipping their arrowheads in feces or decaying cadavers; the latter, by launching pottery filled with poisonous snakes onto the ships of King Eumenes during the Second Macedonian War.(1-3) Plague-infected cadavers were hurled into the fortifications of adversaries during medieval battles and during the famous Mongol siege of the Ukrainian city of Kaffa (now Feodosiya) in 1347.(1-5) Later, the development of the trebuchet, an enhanced catapult, made it possible to accurately launch several-hundred-pound loads of manure or large piles of bodies that previously had been too heavy.(8 ) Although some authors believe cadavers were not competent plague vectors,(5) the prevailing scientific establishment of those times lacked the epidemiologic sophistication to realize this. Biological projectiles had some strategic value -if only psychological- because their use persisted into the 20th century during the Russian Revolution, various European conflicts, and the South African Boer Wars.(7)
Interesting stuff. If you consider the Scythians and Mongols immature for their creative use of poop, you have your reasons and I respect that. However, I would like to point out that their use of poop in warfare was a solution to a problem and was not done just to be gross for grossness sake and getting a laugh (unless that was the entire basis for their wars, which I doubt). I would like to be able to do this kind of stuff in-game, and bodily waste would be necessary for this.
Also, perhaps if bodily waste was in game, pee would have been used by the players as a reagent in dyeing and other industrial applications as in real life (
http://en.wikipedia.org/wiki/Urine#Other_uses). I would like for that to be in game, too