It really just takes practice - and frankly, not that much - to get used to playing an FPS without the crosshair present.
The center of the screen is always there, and your gun pretty much always shoots there... I never understand when people add a dot to assist; to me, it'd be very distracting.
In Medal of Honor: Allied Assault, there is an on-screen crosshair, but it's light and hard to see, and after a little while you don't even notice it - which means you're not even using it - and a lot of players I know turn it off because it's unnecessary; and this is a game that's been around since 2002ish.
Even in the original GoldenEye 64, I have no problem running through a level on 00-Agent (with that atrocious framerate) and picking consistent head and body shots without aiming or a crosshair. I do know some members of The-Elite speedrunning community that use one, but I know quite a few of their top players also don't use one and get by just fine.
It's a crutch - my personal opinion is, it's not really "cheating" like hacking is, but if you refuse to go without it, you'll never really learn to drop the crutches and walk correctly... it's just not needed to be an effective player in this game, especially given the aiming system and spotty accuracy of many of the weapons.
