You are totally correct. It's not just cows either, there are parts of many animals that I did not even know existed until I ate them outside the US. The skin, intestines, blood, heart, lungs, tendons, etc. of most animals taste great yet are hard to find in the US.
When I was a kid, the heart and gizzard were the best parts of our chickens. I only had cow heart once but it was delicious. I never did like liver though.
Many of the other parts are even more unhealthy though. E.g. you can eat the skin, and it's considered a delicacy in Ghana and South Africa, but it's not exactly good for you. Especially when it's doused in poison to keep insects off the cows.
It would be easier to raise healthier herd with smaller population. Going 100% would be unrealistic I agree..
A lot of the organ meats are very rich in both micro and trace nutrients that are quite important. Cooking with skin and bones impart a lot of new flavors as well, even if you discard those parts after cooking.
Last I checked much of the leftovers from animal slaughter made their way into pet food as protein filler, so I wouldn't call it wasted.
What's your source on parts of the animal going to waste? I was under the impression that absolutely as much as possible was being sold or used somehow (rendering plant, pet food, chicken nuggets...) -- anything wasted is just lost profit, after all.
A local butcher who throws away perfectly good beef fat! jokes aside I understand it not all thrown away (some parts are) and used in pet feed, cosmetics, fertilisers etc.. But the primary reason those cows are grown is a human consumption - other uses are an attempt to utilise "free" leftovers. So to reduce number of animals we should eat more other parts.