If you have a pancreas that still produces insulin you may be able to control it with diet and exercise alone. But if there is no insulin to metablozie carbohydrates it is truly beyond your control.
I see patients all the time who beat themselves up (not literally) because they have diabetes, it is not necessarily by choice that folks become diabetic, if you have the genetic marker for diabetes you will develop the disease if you live long enough. You can avoid this for a long time by good living, but sometimes it is just fate, like being tall or short or having brown eyes. You will certainly avoid a lot of the consequences of the disease by following your doctor's advice.