@DeMachina:
Why creating a learning curve, even a small one, when you can keep the mouse movement as it is and make it easier to players.
The mouse was always controlling the field of view, you want to look to the right turn the mouse to the right.
When the weapon is lying on something you should still controll the view by the mouse, the fact that the body is leaning toward the opposite direction, is just a physical thing, that you even do not notice.
I´m personally against the reversed mouse, just my opinion, or make it optional (where I´m sure nobody would use the reversed mouse option anyway). Let the democracy win

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I think it is clear, that when the weapon is supported, the single mouse movement plays the role of the lean, strafe and duck/stand up keys at the same time and all in one, which are usually controlled by the lean, strafe and duck keys.
I mean if your weapon is supported, the body lean would allow you to move the weapon just slightly to the right, or left, cuz a real wide lean would lower your shoulder position and let you aim sideways+up, which is an uncomfortable position at all.
- The body lean (when mouse moved to the left, or right) allows you to turn the weapon slightly to the right, or left.
- To increase the weapon turning radius at all, you have to sidestep with the feets, which makes a circle strafe around the supported point of the weapon.
- To aim up you make a slight duck with your body, to aim down you stretch yourself a bit.
All the actions you do with separate keys, can be done by the mouse, the duck key could just give you the option to duck behind the thing where your weapon is supported at, the manual strafe keys, could make the circle strafe faster, because it is to impractical to make a 150° turn with the mouse (with a key you would just need to hold the strafe key).
On the other hand when the weapon is supported and the turn/lean/circlestrafe used via the mouse, the movement keys (only A,D,W and S) would let you move as usual and release the supported weapon mode keeping your weapon shouldered then (for example you want to escape, just strafe via the strafe key, or move backward via the movement key and you move as usual and don't have to deactivate the supported mode with a key).
The duck should keep you in the supported mode, but make a real and full duck.
To activate the supported mode I think they is no other simple way as to have a key. When you comne close to something where you can lay a weapon onto it (maybe marked with a symbol, or message in the HUD), than push the 'use key' to enable the supported mode.