We have editing and deleting on our forum. No one has ever abused it and I doubt anyone has ever thought of abusing it. Our adim even suggests editing the first page or our build threads if we change the robot, which I have done over year after the post was made. Its good because I could read one of my posts 10 times before I realise it doesnt actually make sense.
But there seems to be more arguments here so maybe your admins are right.