I know someone who freebirthed.
She had no previous bad experience, and had an independent midwife who was available to come whenever she chose, who she trusted completely. She just didn't want anyone around for the actual birth.
She called the mw after the baby was born, though, as she had strong afterpains and was worried about the placenta coming out. The mw came and helped with that and nothing else. If she hadn't had a sympathetic, understanding mw at that stage she might have had to go into hospital, so she was very glad to have her.
I have had two home births with an im and she was wonderful. We built a relationship during the pgs and so she was very in tune with my needs for the actual births. She was in the room but totally unobtrusive for ds1, in fact I have no memory of her being there, my field of perception seemed to end at the edge of the birth pool!
For the second birth her, dh, my sis and I were happily chatting away and trying to get the birth pool to a sensible temperature with hot kettles (we had filled it with cold water by mistake) until about 3 minutes before I gave birth. I then got into the pool, had one contraction and out shot the baby. The total sum of her intervention was to boil some kettles and say 'catch!'.
I think having a birth pool can be very helpful in terms of setting a boundary where you are the one in control. Mine was quite big, so if I was sitting in the middle no one could have reached me very easily!