Guns are only weapon you need in modern RPG setting?

[DontEatRawHagis]

Seriously, try to picture someone suddenly being stabbed in the back. Does a big loud scream make sense in that situation? Or is a sharp intake of breath at the sudden, unexpected pain more appropriate?

Pain exists. If you stab someone expect them to say something afterwards and yell. The illusion that you can stab someone in the back quietly is similar to that of Suppressors on guns stopping noise altogether. Will the scream of being stabbed be heard as loudly as a gun shot, no, but it would probably get the guys in the next room over quickly to hear what happened.

I think if you realized that you were just stabbed in a battle situation you would yell at your allies to warn them. That is, if your allies don't know you just got stabbed.

I don't like Hollywood when they have melodramatic scenes where people get stabbed cough up blood or make little to no noise. Sometimes they stay alive just long enough to finish their monologue, other times they die in a split second.

Edit: Hell even if you use a chemical to try and knock someone out they will be fighting for a long time before it takes effect. Not to mention the brain damage such chemicals can cause.