@armapirx
Don't get me wrong on the subject, I love Arma since Arma 1 the way you do, because of the non Call of Duty style. Pushing the boundaries of the gaming engine even more so.
"With that in mind, all that could be demanded from a player, would be to only hold W and left mouse button, because he plays a trained soldier, whow knows when to move and when to shoot." -Armapirx
This is not what Arma is about, you are right. The skill in Arma lies in the abillity to learn the skill of doing what, where and when, and this is what is so amazing, players that can fly a arma helicopter to unbelievable precision, because they LEARNED it.
Your idea to be able to toggle it on or off (which I didn't read out in your desc. I am sorry) is great, and yes, for those who can and want to a very nice feature.
I have a lot of experience with rifles, as I worked for a weaponsmith for two years, and i am a hunting guide. Anybody using a rifle (or assault rifles) with iron sights or improved sights like Reflex, Scopes or other, can compensate the effects of parallax simply by pratice and it becomes second nature. Soldiers do not think about the parallex effect since they have the experience with it, thus being able to think about more critical things like the tactical situation or scanning for enemies.
I myself would be so focused on the parallax, that I would completely neglegt my surroundings. Headtracking in my opinion is not as precise as it should be to accomodate this feature.