Also, one thing that will surely make me very disliked. But when have I ever shied away from that?
A rider should be as in shape as the horse he or she is riding. If you are very overweight (read: obese), you have no business getting on a horse until you can do the equivalent of the same work you ask your horse to do.
I rode a few time with a French Saumur master and he said as much to me when I was only 12 years old. Hey I felt a little bad, but overall I am grateful for the advice he gave me. I still carry a few extra pounds; I probably always will. I can, however, do the equivalent of the work that I ask my horse to do. It is only fair. There are riders out there kicking and pulling at their horses, throwing them off balance, yanking them in the mouth, bumping them in the kidneys and so on.
I don't care that the horse can carry the weight, that he is strong enough. That's not an excuse to me. You expect your horse to be an athlete, you better damn well be one yourself.