I question a bit whether the Latin stercus has the same vulgar connotation as the English word shit. It of course has the same denotation.
It did appear to be slightly on the vulgar side, but perhaps more like "crap" than "shit". As you can see the difference in degree of vulgarity between "crap" and "shit", so too it's very difficult to know where stercus was on this spectrum of vulgarity in St. Thomas More's day.
But even merda appeared in agricultural and veterinary texts.
We had the lawn guy over the other day, Mexican, speaks limited English, true prince of a guy, hails from Chiapas. I was trying to explain to him that one of the neighborhood feral cats pooped in the wood chip pile (he'd cut down a tree the week before), and to be careful that he didn't get it on his shoes when cleaning up the pile. Seeing that I wasn't getting the point across, I said
"mierda" and he then knew exactly what I was talking about.
Cat poop is like Modernism --- it stinks, it has a way of sticking to whatever it touches, and once it makes its mark, it's next to impossible to get rid of.