I believe QSing is viewed in a negative light because of the idea of it. You take a weapon specialized for ranged combat, and ONLY ranged combat, and give players the ability to use it in a setting which they should clearly be at a disadvantage. Given that this issue has somewhat subsided since MW2 days, it still is viewed negatively because of the "melty" feel to it.
Looking at it another way, it's similar to giving a shotgun user the ability to blast people from across the length of a large map with relative success. It just doesn't feel right.