I have type 2 diabetes, but I feel fine, so why do I need treatment?

Complications. Medications are needed to prevent complications of diabetes, which can be silent (you don't feel the damage of diabetes) and can include eye damage, heart disease (heart attacks), stroke, kidney damage, and nerve damage.
The consequences. Similar to slow onset hypertension, early diabetes can be entirely asymptomatic. The only reason to treat when you feel fine is because you want to prevent complications down the road such as a heart attack, a stroke, loss of vision, or kidney failure.