I posted this not long time ago in another Thread, so I feel free to use it again because it shows my oppinion:
I dont think we need a punish of loosing XP or Gold.
Just remove the Team Damage! and add mirror dmg instead!
That means if u hit a friendly player u get the dmg instead, and the friendly player doesnt get harmed!
Same for horses, if someone hits a friendly horse he gets the dmg instead. Same for teambumps with horses, the horse rider gets the dmg for the bumping.
With that system only the one who does teamdmg gets punished a little bit, but the one who received the teamdmg does not get punished.
Loosing Gold or XP would count as a double punish. For the one who hits his teammate, and for the teammate who gets hit and then probably looses a fight because of low HP.