When milk is separated to make cheese or extract protein, etc., it separates into two parts - casein and whey. These are not the same thing, and whey protein is actually a much better source than casein.

As for how much total protein to consume .5g/kg is on the low side. For a 80kg man (176 lbs) that would mean only 40g protein a day. Even the USDA (which sets minimum values as the levels necessary to prevent disease, not the levels for "optimum" health) recommends 65 gr/day for a person that size. Increasing your protein intake can help you moderate insulin levels leading to a lower body weight and better glucose utilization for better energy sustainability. Excess protein does cause kidney and possibly liver damage, and high protein foods often contain tons of saturated fat. However, I wouldn't worry as long as you eat 1.0-1.5gr pro/kg body weight per day.