YA ok, so everytime someone gets hurt they just kill themself to stop you from getting the kill.

Assisted Suicide is a special case that exists in order to prevent people from killing themselves in order to deny the other team points.

CoD doesn't use a point penalty for suicide.  Regenerating health reduces the chance that someone will intentionally kill themselves to deny someone else points, but it doesn't eliminate it.  (Particularly actions like jumping off a ledge while under fire.  If you aren't hit, you survive the fall.  If you are hit but survive the bullets, then you suicide.)  Or that people might take more intentionally dangerous acts if they think they'll get themselves killed before an enemy can get a kill on them.

If Assisted Suicide didn't exist, then it wouldn't take long for people to start complaining that they were being robbed of their kills.

You could also argue that self-inflicted wounds are the real special case, not Assisted Suicide itself.  (HC also has a special case for team inflicted kills, with ricochet, and a 3 kill kick rule is also such a special case.)