Certainly as far back as WWII, and there are various, though never fully documented cases of Omar Bradley expressing his disdain for snipers.

"General Omar Bradley held a very bad view of the snipers his men were facing and privately he was known to condone the killing of captured snipers, though this was never put into an official document."

Source: Stalkers and Shooters, p. 130. Dockery, Kevin.

There is a quote, often attributed to Bradley, that ends along the lines of "You can't spend all day shooting away, then throw up your hands the moment someone comes up on you; that's not how you play the game." This disdain for Snipers is a fairly common refrain in the ETO and MTO; a rather indiscrete comment from Patton (Surprise!) prior to Operation Husky (being in summation "Kill any Sniper you capture, boys") was actually used as a defense in the war-crime trial of two Sgts in 1943; who claimed he was simply acting out on 'documented' orders to kill Snipers. Famously, Patton sided with the man, but Bradley pressed charges. Point is: Generals and Commanders in WWII, especially in the ETO, were not exactly fond of the idea and tactics behind sniperism.

It has me thinking of similar comments on skirmishers and sharpshooters from men who saw their necessity, but disdained their tactics; such as Frederick the Great. The common chorus of disdain for a soldier or unit that doesn't 'stand up and fight' figuratively or literally isn't at all uncommon throughout history.

I think its the psychological difference between seeing your killer; and thus having the idea, real or imagined, that one is still in control of one's fate, compared to say, a random 'accident' of being hit by artillery, or dying a sudden, uncontrollable death by an unseen shooter. It doesn't exactly invoke the most sympathetic emotions in a fighting man to suggest that a man can kill but not put himself in any perceived danger.