The biggest thing that gets to me about the whole realism argument is the amount of people who seem to pin "being shot once" to realism. Honestly, it is getting to me that so many people think the speed in which you die is the sole feature of 'realism.'
The biggest, and thinking back on it maybe the primary reason, thing about realistic games are maps!
Seriously, the far more realistic game systems out there have maps that are truly open ended. These are maps where the sniper could be located in one of a dozen windows facing your location, maps you can't just rule 99% potential MG nests out because they are 'boarded up' or 'can't be see into because of a curtain,' Maps where a single chest high fence isn't going to force you to talk into the enemies 'kill zones.' Realistic games tend to produce realistic maps.
Maps where you CAN flank a MG position instead of having to do the whole 'throw many re-spawns into the meat grinder so someone can get a lucky shot off' tactic that only generals that never leave the pentagon think of as a good plan.
That is what FPS are missing for me: The ability, and even requirement, to use the very tactics that our military forces MUST use because... trying to act as if your in a game, with unlimited lives to throw away, leads to failure more time then not. Taking a 'hard core' mode doesn't magically make the game 'realistic' because you no longer have a hud.
It just makes it less like an arcade game, but still no closer to realism.
So yeah, I am pro realism for the simple reason it will give us maps requiring realistic tactics to beat. Maybe killing that whole run and gun game-play that many gamers use today, simply because it means they don't have to work as a team and can hold to the delusion that they are too important to listen to orders.
Added On that note:
Hell, with the current set up your penalized for putting the team above yourself. The person who holds a position, suppressing the enemy long enough another person can flank, gets zero credit for doing all the work in today's game. All the credit goes to the person flanking for having all the skills required to shoot someone in the back and not the person actually getting shot at.
Things like this is why we can't have realism in games: Who the hell is going to ruin their own personal score just because they can obey orders to let someone else take the glory?
Games designed to reward kills lead to players unable to work as teams, cause they view team mates as a threat to their score. With no reward for working together, and all rewards geared towards 'lone wolf players' then it is just too damn likely for team work to go out the window. Without team work... you can NOT design a game where realism is required to win.
So much is stacked against the realism community and worse is they don't redesign games from the ground up as needed to eliminate this mindset that is killing our games.