@ShotgunSheamuS: knife melee could be stealthy, however even at close range guns probably have the advantage.
Knives have to be stabbed into someone, past ribs, etc, however guns instantly send a bullet very deep into someone (or completely through them).
Knife kills are fine but I'm not a fan of "takedowns", etc. I think if you sneak up behind someone, you should have to stab them multiple times.
This could be quick and relatively quiet, simply "clickclickclickclick" and they die before they can even turn around.
However if someone "charged" you, they would be unable to easily kill you with an "automatic takedown", since the target would naturally run away / shoot back and kill them.
Think about this: why would a stab with a knife be somehow "inherently" more lethal than being shot with a .45 or a 9mm? Realistic answer, it wouldn't be (although pistols would be pretty ineffective if ArmA 3 properly modelled body armour).
I don't think knives should be something unusually deadly, sneaking up behind someone with a knife should be about as damaging as sneaking up behind them and shooting them. That's fair and it's also pretty easy to do, instead of pressing one button and instantly killing them.
I'm not against melee combat, I just want it to make sense (within the ArmAverse). If I can't kill someone with a single handgun bullet (excluding headshots) then I shouldn't be able to kill them with a single stab.
I also think knives should include some skill and a normal chance of failure, which automatic takedowns either do not include, or do so in an unrealistic way...