If the horse is used to being barefoot, there is no reason to put shoes on it. A barefoot trim, done correctly is actually better for the horse than having shoes on. But it also depends on what you are planning to use the horse for. Anything where you are on soft to med-firm ground, barefoot is great. But most horses require shoes for traveling over rocking ground, especially if there is no rocky ground in their pasture for them to get used to walking on it. But if you really don't want to put shoes on him, you can always used the boots that have a protective layer that acts like shoes, but you only put them on when you need to.
I actually prefer barefoot to shod, it's more natural, and in my opinion better for the horse and their feet.