There used to be a rider at our barn that insisted he had perfect
control over his stallion riding only in a halter. Most of the time he
apparently did---until a little girl came riding along on her little
mare, who was in season. The stallion paid more attention to his
hormones than to the halter, mounted the mare to breed her, crashed a
hoof down on the little girl and killed her. Granted, this is as much
or more an example of a stallion who hadn't been taught when it is or is
not OK to be a stud as it is a case of a halter being insufficient.
I'm not saying that riding in halters is or isn't OK, but speaking ONLY
for myself, I prefer having a bit in Cato's mouth, and if you do choose
to ride in a halter, it should only be done on some really well-trained
horses, not just because it's more convenient at the drinking trough.
Susan