Acceleration on PC is generally a bad thing. But since both sides have said their piece and you understand what acceleration curves are for, let's talk about why it's not a bad thing on console.
On PC, good FPS games have native mouse input. This means the game does not use Windows to feed the mouse input signal, as the game takes the signal directly from the mouse. This results in 100% mouse sensor accuracy. What you see on screen is a direct result of your mouse sensor. This allows incredibly fast, or slow, but accurate movements. Native input is THE way to play with a mouse on PC. If the game doesn't support native input, pros won't take it seriously. Because of this, acceleration is frowned upon. You can move as fast as your sensor will allow, and still make incredibly accurate fine micro movements. No acceleration is needed.
Now let's flip over to console gaming.
As we all know, console games are restricted by the controller maximum velocity (maximum turn speed). This cannot be raised or bypassed. There is no such thing as native mouse input for console. This means our mouse is just emulating a joystick. The XIM does an insanely good job at this. So good, in fact, that some games aren't playable at the 1:1 ratio. Titanfall is a perfect example of this. The game has a low maximum velocity, and the result is a high XIM sensitivity will have you hitting that turn cap too quickly, while not allowing the micro movement accuracy.
This is where a curve comes in.
A curve basically tells your XIM to maintain the 1:1 velocity up until a certain point. You control these points, where the sensitivity gain increases. In doing so, you can craft a configuration that will resemble PC like feel, with acceleration. It will not be 1:1... But you'll find it more enjoyable on a low turn speed game. Granted, you will still hit the turn cap regularly, but the difference is your accuracy is boosted.