So, after /tg/ recently had a rather lengthy (and lively) discussion about the pros and cons of slings and why they eventually fell into disuse, why not warm up the topic again on /his/ so we can all be angry at each others opinion?
IIRC the main cluster of the argument was that slings should logically still exist as side-arms even if the user has a different primary weapon because they are so small, light-weight, and have more-or-less infinite ammo in that you can simply gather larger pebbles from the ground and launch them with a sling.
Against this, it was argued that slings require significantly more training than other ranged weapons to be used effectively; that even a well-trained slinger could not shoot with the same precision than an archer, that slings lack penetrative power against anything but light armor, and finally, that slingers could not fire barrages from behind infantry lines and thus had to expose themselves as skirmishers.
TL/DR: Why did slings (not including staff slings) eventually disappear from post-antiquity European and Asian battleground?