Although the game supports analogue input for movement (joystick/controller) on foot it seems to be limited to the same 8 directions and set speeds as when using a keyboard. This makes it feel rather unnatural as the game does not respond to the subtle inputs an analogue controller can provide.

Analogue movement allows greater freedom and more accurate positioning for shooting round corners, peeking over hills etc. It also allows for more natural movement (smooth transitions from forward to sideways movement) when clearing stairs, looking in windows and so on. Once you're used to analogue movement going back to WASD feels so clunky.

BF3 does this properly, and of course every console game does too.

As far as balance and fairness goes the game already supports enhancements for peripherals beyond keyboard+mouse, like TrackIR for improved freelook and lean and analogue control of aircraft and vehicles.