Wow.. you are using your head today aren't you hahahah. Do you honestly think they are going to test humans to see if insulin is anabolic. Think about it. What normal person would inject something into them that could possibly kill them.
They have in fact tested this. It is NOT anabolic at physiological concentrations or any concentrations you could achieve by injecting insulin (without dying). At several thousand times the physiological concentration it's anabolic, presumably by activating igf-1 receptors. This is not relevant to us since this can not be achieved.
Insulin is anti-proteolytic ("anti-catabolic").
I don't see any physiological reason why injectable insulin, in the doses most use it at (which are very physiological doses, not supraphysiological), would ruin a physique any more than eating a high carb diet.
If guys are coming in too smooth I think it's simply because they don't want to sacrifice size for cuts, not the insulin per se.