Although I do agree with the fact that a rider can do damage with any kind of bridle (equal with any person, bit or no bit) I also agree with people saying that a rider riding bitless can be much gentler and most likely more gentle than somebody riding with a bit.
Definitely not true on the 'quicker response' bitless, or most gentle riding gear for head being bitless, part of this statement. My mare is trained with rope halter (bitless), in an english hackemore, snaffle, and she's done a bit with a mild curb (we're not quite "there" yet relaxation wise, for the curb all the time). Out of the first three, the one that I get the "instant" response from as soon as I shift the rein, is the snaffle. Simple reason being the mechanics...the snaffle is in the mouth, and the mouth a bit quicker response triggered by slight shifts in the reins. All I have to do is close my fingers around the rein, and she is responding. With the halter, while she responds quickly, the response is definitely not "that" quick...I have to lift a bit before she feels the movement, and responds. Again, another mechanics thing...the bridge of the nose isn't nearly as sensitive to the pressure as the mouth is, so the response time is diminished, no matter how well trained the horse is.
True, bitless (depending on the TYPE; are you talking the rope halter, indian hackemore, dr. Cooks?) could be gentler in the sense that you aren't going to damage the horse's mouth at all, BUT you will still be putting poll pressure, face pressure, chin pressure etc (again, depending on style bitless), and you can easily deaden those areas, just as easily as if the horse were being ridden with a bit, and having his mouth deadened to pressure. I don't care what style bit, bitless, or halter a rider uses, personally, as long as they are used properly, that is what counts, and I really don't feel that one is SO much better than the other. If any horse had his choice, he wouldn't be ridden period, so none of this is 'natural' anyway!