The whole-body impact of type 1 or type 2 diabetes can affect eyesight, heart function and kidney output. It can lead to fatty liver disease, skin infections, osteoporosis and even dementia. No other disease--except perhaps an autoimmune disorder--carries this kind of whole-body risk. Clearly, losing any of these capacities risks your pilot privileges, let alone several at once. Diabetes is items 18K on the FAA's Basic Med Checklist.
This is a companion discussion topic for the original entry at https://www.avweb.com/flight-safety/healthy-pilot-9-diabetes-and-your-license-to-fly