Why do people hate quickscoping?

i know that there are 5 year old kids that say "oh your bad kid cuz you hardscoped" and that looks bad for quickscopers but kids like that aren't representatives of quickscopers. i don't see how quickscoping is overpowered (maybe in mw2). i do know that there are snipers that basically ruin their teams chances of winning but there are a lot of players that do that not just quickscopers. and people have misconceptions about quickscoping; you are supposed to aim down sights but you're supposed to only aim long enough to where you can see the enemy in your cross hairs so it happens in a split second. enough practice can make it a legitimate way of playing.