But pinning a guy against the cage and elbow slicing his dome into what resembles a Saw movie victim is?
All effective strikes are 'martial arts' - headbutts, throat punches, groin shots, etc.
The rules just place limits. If kicking a downed opponent to the body is legal and fine for the viewership, then its not that different to the head. but I understand why they are banned, even though I like them. Its just where that line is.
Personally I'd be happy if kicks when BOTH fighters were downed i.e. upkicks to the face from guard, not having it is totally unbalanced, and kicks to the face to defend heel hooks etc. and knees to the head at any time.