Why would a doctor want to do a colon resection on a 46 year old man with no history of colon problems?

Red flag. Surgery is done for a significant benefit to the patient. A risk/benefit analysis is part of the consenting process before any surgery. So if it is not very clear why the surgery is being recommended, then get more information; check out a second opinion, take family/friend with you to discuss the procedure before consenting. Be well.