It's not about teamkills.
It would turn teammates into enemies and enemies into unharvested wheat.
A lot of people played, very few complained. Why don't you just admit that you didn't like how thing were going and that you decided to change it.
What do you mean, admit? As if I'm trying to hide something? Of course I didn't like how things were going. It was the most horrible gameplay every, and I was about to just leave the mod. Killwhores got levels faster, resulting in killwhoring more. Normal people or peasants got behind and could never catch up. People were stacking AGI so they could outrun teammates and fight enemies alone for the XP. People were trying all kinds of tricks to prevent their teammates from getting into a fight. It was one fucked up gameplay.
Then came the area of xp, which had it's trouble too, but was far, far, far better than the xp per kill system.
So yeah, never, ever, xp per kill. Don't even bother.