I recently came across some back and forth between Art Chance and others regarding the need for documentation of the fact that (at least) some Civil War soldiers intentionally removed the rear sights from their Enfield rifle muskets. Those countering Art's assertion that this sometimes took place have made some valid points. Nonetheless, I believe I may know the source of Art's information. I read this some years ago myself, and to date it is the only such reference appearing to document the intentional removal of Enfield rear sights by at least some Confederate soldiers.
In "Life in the Confederate Army -- Being the Observations and Experiences of an Alien in the South During the American Civil War" by William Watson c 1887, (pages 342-343), the fact the some C.S. soldiers of the 3rd Louisiana Infantry intentionally removed the rear sights from captured Enfield rifles and Belgian rifles (page 301) at the Battle of Pea Ridge, and their reasons for doing so, are described in detail.
In summary, according to Wm. Watson who himself was a member of the 3rd Louisiana and relates the information, some Confederates who after the battle retrieved Yankee Enfield rifles, Belgian rifles and Colt repeating rifles from the field (the two former equipped with raised sights) noticed that all of the sights had been set for 200 yards. Watson states this accounted for the Yankees shooting high as the Confederates closed the distance to 40 to 80 yards to be effective with their own smoothbore muskets. Watson continues this was "one of the chief reasons why we were not cut to pieces while fighting so long against a superior force and under such a tremendous fire as we had done on the 7th."
"This led to raised sight being condemned by us, and they were taken off, and the line of sight set to range with the line of fire at about 70 yards -- it being considered simpler and better when the distance was uncertain and constantly changing, for men acting on their own spur of the moment to learn how to aim, high or low, according to distance as they were now in the habit of doing, than to stop and calculate the distance and alter the sight for every shot."
"Raised sights, it was considered, might do very well for sharpshooters, or in circumstances where the object was single and continued fixed, and time could be taken to calculate the distance, and set the sight to suit it; but in the hurry-skurry of the battle, in front of an enemy rushing to and fro, was not a very good place for making nice calculations, and moveable sights were there quite useless and in the way."
This, of course, does not mean that other good reasons do not exist for some extant Enfields lacking their rear sights -- and certainly does not mean that many/most Confederates followed this practice. But it does seem to indicate that their removal was purposeful on occasion, at least by some Confederates.