My horse can be ridden in a halter but not a bitless bridle. It just confuses her. I mainly bit her when we go out and about but if it's just a hack around the farm I get lazy and just the rope halter :)
I don't think all horses can be ridden bitless. There are horses I know who I don't trust WITH a bit let alone without one.
IMO all horses are different and so are people. Some people are far to heavy handed with bits and some use them the way they were meant to be used. Personally I wouldn't be happy with a horse that needed anything stronger than a snaffle and would rather get it re-trained than pop a bit in that I didn't know how to use. :)
I am her eyes, she is my wings. I am her voice, she is my spirit. I am her human, she is my horse.