Sniper do indeed have penalties for close combat, if you miss you die. All you have to do against a sniper in close combat is to make an evasive maneuver to make him miss his shot.
SMG takes a punch from distance damage falloff.
They do not.
Case 1: Sniper in close combat: If a PLAYER misses, he dies.
Case 2: SMG tries long distance shooting: If you try to do headshots with an SMG across the map, you need to do more headshots to kill him.
Case 1 is player skill limiting him from getting killed. There are no additional penalties for his weapon.
Case 2 is a game mechanic limiting SMG effectiveness over range. Thus adding an additional penalty.
If you die in case 1: it's because you're not skilled enough
If you die in case 2: it's because the game limits you from shooting at longer ranges by reducing damage.
Last fact: 90% is discussing against you, meaning that the MAJORITY of people are against any form of quickscoping in this game. (I'm not saying that you shouldn't defend your point of view)