There are many factors involved in whether a horse can go barefoot or not. I have listed them below.
1. Health of the foot:  Unhealthy hooves are a very common problem. Some horses have flat feet and must have hoof protection.
    Causes of flat feet:
       a. Shod too early in life and feet could not develop.
       b. Improper trimming early in life, or throughout life, where sole was
           routinely removed and cannot grow back.
       c. Diet. Too much sugar/iron can cause breakdown of hoof
           wall connection causing internal structures to drop withing the
           hoof.  This can be reversed  in many horses simply by adjusting the
       d. Metabolic disorders.  This is also a very common problem. Many
           horses develop insulin resistence (diabetes) from being fed too
           much sugar throughout life. Horses weren't designed to eat sugar.
           Some breeds are more sensitive to sugar than others, just like
           humans. Paso Finos are the #1 breed to develop insulin resistance.
           So stop feeding sweet feed! Grass is also very high in sugar and
           should be limited in the horse's diet. Horses evolved in dry climates
           and are designed to eat a variety of plants and dry grasses.
2. Type of terrain:  If your horse has a healthy concave hoof and your type of riding consists of light walking and trotting over mostly dirt and grass and occasional gravel, then it should be fine barefoot. But, there may be times when you want to go on a weekend trail ride where there are rocks or gravel and you may be riding for hours at a time. Once again, if you are just walking along and there's an occasional rock here and there, your horse should be just fine. But if you will be riding on gravel or just don't know what the terrain will be, be safe and either have your horse shod or be prepared with boots. Boots are easy enough on the front feet but I avoid booting the back feet because, in my opinion, it's a huge pain in the ***. They don't usually stay on and I think the horse isn't nearly as sure-footed with boots on the back.
3.  Type of riding: If you're the type of rider who rides hard, the Glove boots are ok, but the Eponas are better.  If you ride fast and hard, and your horse's hooves are concave and healthy, and you are riding on dirt or grass with few rocks, then you'll probably be ok barefoot.  But, no matter how good and healthy your horse's hooves are, if you ride long enough on any type of gravel or rock, the feet will become sore. We ride pretty hard and fast and I keep Eponas on my horse's hooves. Leaving metal shoes on all the time is a bad idea because they are rigid and don't support the whole hoof (only the outer wall). They restrict blood flow and the horse's hooves grow slow. The Eponas support the whole hoof, are flexible, and actually help the hooves become more healthy by stimulating the hoof. We noticed that our horse's hooves started growing extremely fast with the Eponas applied, which is a really good thing.  
1. Horses are healthier barefoot.
2. Not all horses can be ridden barefoot.
3. Flat footed horses will always need hoof protection for riding.
4. Metal shoes are OK occasionally, harmful if used too often.
5. Not all horses can wear hoof boots.
6. Epona shoes far out-performed hoof boots.
7. Epona shoes can be left on without harming hooves.
8. Hoof boots are cheaper but not practical for fast, long distance riding.
9. Diet and proper mineral supplementation play a huge role in hoof health.