I'm happy to have been able to help shine some extra light on the matter. Trust me, I know very well how things can look one way and one can be sure that it is that way, but its not. That's why there are so many sects of Christianity and even multiple sects of Judaism.
You also raise a good point about portions. Because in the western diet, meat is the centerpiece. In the Asian diet it is more of side served in smaller portions for flavor. And so, although we know that there were, of course, gluttons, it was not supposed to be consumed in large portions like that. If there were any exceptions, it would be, as you said, to avoid wasting meat. I would also add that every man also includes women and children which is also why the portion size would vary. I'm sure you already knew this but some misogynists out there tend to try and disqualify women from being included when in reality the word 'adam' applied to all humans.
And actually this was also true for other cultures like Egypt. It has been theorized that the reason why the firstborn died was because they ingested a larger portion of meat from animals that were tainted from a previous plague. The theory goes that the plagues were all connected to each other and couldn't be stopped. One day I'll probably start a thread about it.
You are also very much correct about the law as it applies to dead bodies. All corpses are considered unclean. Regular people can touch unclean things, but then the unclean thing makes them unclean for a set period of time. Of course the most famous example is women being unclean for their menstrual period and having to set themselves apart so as to not make anything else unclean by touching it. Of course their level of medical knowledge left a lot to be desired so they had to avoid microorganisms and bacteria with an almost superstitious level of fear. Dead animals and such have caused many plagues in human history because when the body dies the living organisms in the body do not die with it. Instead, they take over the body, feed on it, which is what helps it to decay and return to the "dust". This is why we cook food. This is why "raw water" is a very bad idea and can kill you. Even ancient people had enough sense to know that there was some kind of invisible threat associated with death and decay and that it could be passed by blood. This is why kosher meat isn't the same as regular meat.
Just because I'm saying its okay to eat meat doesn't mean all meat is equal. The kosher process is a higher standard of making sure the meat is safe to eat. Do I personally think its necessary? Not in 2019. For a long time now, animals have been getting treated with antibiotics so that people don't get sick eating them. Companies don't want to get sued so they have a "market forces" motive to make their product safer.
Notice I said safer, not safe. Nothing is really safe; including plant products. Even if they say its vegan or its organic, a lot of these labels are marketing lies. And while it may be better to grow your own stuff, there are pros and cons to that as well. But... my point is that ancient people didn't have all these medical advances. So their meats were more prone to having issues that would make them "unclean".
And yes, "how it died"... that is of supreme importance. Even today, we don't eat sick animals.
Now... I did a whole study on this a long time ago, dealing with how "unclean" wasn't the end of the world. It basically just meant "unhealthy" as far as they understood health and things that would cause them to get sick. Men were literally afraid of women getting them sick and made them separate themselves. Well you wouldn't do that to your wife or girlfriend because you know more about health than they did. And we have soap and shampoos and wipes and all manner of antibacterial products and things they didn't have. So you have to consider the affect of technology.
What was told to them was told to them for their time and their environment. That's why in the garden they were given a different diet because the garden had enough nutrition among all the fruit trees and things that they didn't have to toil or hunt. The garden had everything their bodies need (is my belief of what is being conveyed and can also have referred to fruit that is now extinct or that only existed in the garden that could have produced later myths like Ambrosia). But after they were removed from the garden that ease of survival was taken away. And now they were faced with deserts and wild animals; possibly even climate changes. And then when you consider the flood it would have been impossible for them to survive without meat because plants needed time to grow back after being drowned and receiving no sunlight. So whatever vegetation the region might have had... was no more. So those clean animals were very necessary for their survival. And they had to eat on that boat too. (This is my view of hypothetical story as presented by the bible. I'm not saying I believe it.) And that's why they already knew what clean animals were before the time of the flood.
I'm not saying meat is the ideal food. I'm just saying it is what it is. And there wouldn't have been so many rules about meat if it wasn't seen as an important part of their diet, instead of saying "meat has these cons so we're just not going to eat it at all."
One of these rules was about 'Chelev'
Speak to the Children of Israel, saying: You shall not eat any fat of an ox, sheep, or goat. The fat of carrion and the fat of an animal with a fatal disease or injury, may be used for any work, but you shall not eat it.
We know that fat isn't good because it will turn into cholesterol and clog your arteries. If you have high cholesterol you should definitely stop eating meat. But also, if you fast periodically and eat correct portions for your size and you avoid the fat as much as you can, then you should be able to avoid this problem. I don't want to overstate this stuff. I just don't want people going crazy on meat because I said it was okay. No, it's okay in MODERATION.