Except it doesn't matter to a large percentage of the anti-sniper crowd because it isn't the weapon that is causing the problem.
"I hate OHKs, that's why snipers svck"
Problem is that in most games with one hit SR HS kills you can put down an opponent with one trigger squeeze from ARs, SMGs, and LMGs just as easily and you don't even need to hit the guy in the head. So why is the sniper's kill such an atrocity?
"Quickscopers svck"
It's an exploitation of a flawed game mechanic, and it's still pretty close to running around with a shotgun that kills in one from close range. It wouldn't even matter in Brink since non-ADS fire is just as accurate as ADS fire.
"I can't see the guy shooting at me, or I can't get to him because he's over there"
That's the problem with "actual snipers" that people express most of the time, but why would I want to let you see me with any weapon? If you can see me then you can shoot me, and I don't want you to shoot me. What is so wrong with me not running out into the open so everybody can see me when I kill you?
You will notice that I, nor many of the people here, nor SD have never said that OHK snipers are inherently unbalanced. What I am claiming, and I can provide SD interviews to back me up on this position, is that OHK sniper rifles make the game less fun for everyone but the ones using them.
The reason that OHKs, especially at a range, are such a buzzkill is that they don't give you a chance to struggle or fight back. With an assault rifle, when you get hit the first time, you have a chance, no matter how small, to try to survive the firefight. When you are killed in one shot, you don't have a chance to get excited or do anything about it, you're just on the ground looking for the reason why.
I can see three immediate problems with your defense of quickscoping. Its an exploit, you said it yourself, it wasnt intended to be in the game. You can get banned from games for abusing exploits, depending on what they are, why is this one so kosher?
There is a major difference between quickscoping and a shotgun, a shotgun cant kill you from across the map. Being able to quickscope removes what is supposed to be the biggest weakness of the sniper rifle, close range shootouts, and turns it into a strength, completely unbalancing the weapon.
Lastly, pointing out that hipfire is accurate in Brink is hurting your argument rather than helping it. If the sniper/long rifles have the close range accuracy penalty removed, should they still have OHK damage? Especially in a game that takes more bullets to kill than most of the other ones out there. If they had a OHK light weapon that was accurate from the hip and out to any range, why would anyone use anything else?
And on your last argument, again, its just not fun to die when you cant fire back. If it is literally impossible for anyone to get a shot on you due to sheer range, there's just no way to have fun. Its not really a flaw on your part to use the most effective strategy you can, but from a developer standpoint, its bad to have impossible situations for the players in the game.
And in all of these respects, it IS the weapon that is causing the problem. In Brink, long rifles will, for the most part, take more than one shot to kill. At the very least, this will give players the chance to struggle to survive before the last of their health is taken away. Long rifles also do a lot more damage to the head. If getting knocked down to 20% health means that someone hit you in the head, its not nearly as annoying as being hit in the toe. Its not the sniping skill-set that ruins fun, just the fact that the weapons are OHK in most games.