True, meat items will decompose ... I think the main problems, though, are odor (if you ever left a raw chicken in the fridge too long you will have an idea about that
) and the fact that it will attract wildlife and domestic carnivores. Many,
many years ago my ex-husband and I had a large garden and also had a bounty of smelt and suckers (fish); as in, buckets full of them... so, we figured if the Native Americans planted fish with their corn long ago, why not us?? "Why not" turned out to be "oh, because now the skunks have dug up our entire garden..."
(no more meat or dairy products in my garden or compost, EVER!)