Basically, Jason was saying that high levels of insulin causes insulin resistance which causes type 2 diabetes. Treating people with type 2 diabetes with insulin, who already have excessively high insulin levels due to insulin resistance, only makes type 2 diabetes worse, even if it does reduce blood glucose levels.
High insulin levels causes water and salt retention which leads to high blood pressure.
High insulin levels are associated with increased risk of cancer and heart disease.
It looks like high A1C levels for people treated with insulin have a higher all cause mortality due to increased glucose toxicity, but with lower A1C below 6% (42) mortality goes up due to increased insulin toxicity. So, taking lots of insulin to give very low A1C values is counter-productive for type 2 diabetics as it increases risk of death (from heart disease, strokes, cancer etc).
Mortality rates for people with type 2 are higher when treated with drugs which stimulate insulin production like Sulfonylureas and higher still when treated with insulin. The ideal drug to treat type 2 diabetes is one which lowers blood glucose without raising insulin. Hence Metfomin does better in the studies he mentioned. Of course, low carb diets and fasting lower blood glucose very effectively too without raising insulin levels.