Unfortunately, FPS melee attacks have become the most powerful weapons of the game. Designers are too focused on giving players a 'last chance' weapon and they have made these weapons too powerful, a reusable one-shot kill. I agree that the knife is designed to reset the distances between two opponents to what it should rightfully be, but just because it's designed to do that doesn't mean that is what people are using it as. A hammer is designed to drive nails, but that doesn't mean that it can't be used to bludgeon a pelican to death. NEVER UNDERESTIMATE THE INGENUITY OF VIDEO GAME PLAYERS THAT ARE LOOKING FOR A COMPETITIVE EDGE.
There are players who tweak out their characters to take advantage of what the designers are offering in order to give them an advantage; there's nothing wrong with that. However, I've often wondered how a knife wound to the ankle is able to instantly kill my adversary, or how a knife can mysteriously bypass all the canteen, gear, uniform, extra ammo, secondary weapon, and body armor that protects my character from BULLETS. Aside from magic knife blades, I've often wondered why programmers/designers offer ways to enhance the close combat fights, but no ways to protect yourself from them. Hey Modern Warfare, how about next time you offer a perk (titanium/fiberglass underarmor bodysuit) that makes knife attacks mostly ineffective? It wouldn't do anything to stop a bullet, but it would force the "witch-blades", "ninjas", and "slashers" to actually shoot their guns in a First Person Shooter.
How about EMP rounds that dissipate energy swords?
How about requiring multiple knife wounds to kill an opponent (you could then add perks to decrease the number of strikes to kill or decrease the time between strikes)?
How about giving different strengths to the frying pan, crowbar, machette, katana, cricket bat, and all the rest so I know which one to use against the Tank, or Jockey, or an effective Charger?
How about giving the Modern Warfare collapsed victim 5 seconds before they die (by bleed-out) to shoot their assailant, you could call it 'knife-victim last-stand' (a additional perk could also allow the slasher to instant kill)?
How about all designers stop making bullets LESS effective than their real life counterparts, and stop making knives MORE effective than their real life counterparts?
There are things that designers can do to return balance to the popular FPSs and return melee weapons to their designed functions as 'last chance' weapons.
Another major innovation that has infiltrated its way into games is the level design has changed over the last few years. I still fondly remember a vast, horseshoe-shaped, canyon multiplayer map in the original Halo, or the sprawling areas of Battlefield 2 (for 360). It seems to me that designers are designing levels that encourage the in-your-face confrontations that make melee fights unavoidable. I understand that these levels are programmed in an effort to maximize realism and excitement while avoiding hardware limitations, but the choice of forcing all of these fights into battlefields that can be measured in acres (as opposed to miles) is that you are encouraging certain types of play by making those tactics more effective.
Players are gonna play and haters are gonna hate. We can all wish that everyone would have a sense of fair-play and fun, but many are only concerned with their win/loss ratio. Until the designers realize that players will not always use a feature for its intended purpose, we will have to suffer the wrath of the melee-focused FPS players. I just hope that the designers realize that FPS games, like real life, are in the midst of an arms-race, and will start to add some anti-melee features to our favorite games.