Personally, I think consumption of more than a few ounces of meat per week is unethical, by the same logic. It's not necessary for health. However, most people in my country don't have the food culture necessary to make adequate non-meat-based dishes. We weren't all born in a family where we were taught thrifty cooking techniques. So it's a strange gray area of "unnecessary". One doesn't need to eat more than a couple ounces of meat, but one needs food and if one doesn't know how to cook plants into something that could stand in for meat in a satisfactory way, then they "need" meat.
The internet is there, so anyone could do it though. I think whether it's ethical comes down to how much free time you have and how comfortable you are with cooking. But again, that's my personal view. I wouldn't expect someone else to live by my ethics. I would expect them to have some measure of "need" in their scheme though. If their habit is "I eat as much red meat as I want I don't even think about it", unless they're and abuse victim or something that's probably not an ethically defensible position.
The waste is almost entirely on the consumer side.
But when does that happen? Wouldn't the butcher or supermarket usually sell most of the meat and the rest of the carcass is used for dog food or whatever?
I suppose there is probably some waste, but I find it hard to believe there are animals left to rot as you describe simply due to economics.