I've never really seen them as a reason to complain for two reasons:

1- there are worse things wrong with the game like hacking and akimbo mo's

2- how often do you actually run into somebody that is actually good good at quickscoping? Not very often if you're being honest. You may run into quickscopers quite often but only about 30% of the time (random percentage, ftw) do they actually hit you on their first attempt. You see videos like the krypt hacker all the time firing off three or four quickscope shots before actually hitting their target. That's why I don't complain. They lack precision.

Why thank you, mister blunt weapon

When the glitch where you shot your XM25 in the air and then shot down on the ground and you would kill everyone in the enemy team was out, he made a video saying to do the glitch so treyarch would patch it. Why teach people how to do it?