I don't really use the term desensitising, but understand what BlueBird is saying. If I have a green horse I would expose it to everything that I would expect to meet on a hack as I need to be able to be able to be in control out in public so as not to cause harm or danger to anyone else (or myself and the horse). I would spend time getting the horse familiar with all traffic, people, dogs, cows, birds in a reasonable safe environment before venturing on to busy public places. If I didn't do this then I think I would be socially irresponsible and liable if my horse was unsafe and caused problems to others. Of course they will always shy at something, but it is up to me to keep that to a minimum if it affects others (and over here, any riding out on hacks will involve others as our country is so small).
With reagards to "riding through" I think we all are capable of being forceful and using our bodies to control and encourage a horse to do as we wish, but sometimes that requires the space (for the horse to move) which may not be available. If my horse objects to something and arses about in the road, I cannot hold the traffic up while I deal with it and ride through, I will have to get out of the way.