Yes, absolutely. There was some study done showing that gelding kept with only other gelding and no mares tend to be more nervous or sleep deprived or something like that. Also, if your gelding can't handle being around mares, (and vice versa) they need some more training. There is the rare horse that really truly can't handle them, but 90% of the time with good training and handling they will get over it. Also, it's not like you can just avoid mares (or geldings if you have a prissy mare). What if you come upon a horse if the opposite sex at a show or on the trail and your horse just flips out?
“Good things come to those who wait… greater things come to those who get off their ass and do anything to make it happen.” - Unknown