Firstly, don’t get me wrong, I don’t think people should be eaten alive or against their will.
However, in theory, we want to continue our species. If someone has already died, wouldn’t it be normal to cook and eat them?
I think some tribes already do this, but in western societies it’s considered taboo and weird. In reality it makes sense to me if my body is used by my family to give them energy directly. I am passing on directly to the people who I raised.
Obviously I’m not suggesting that we en masse switch to doing this. There are religious reasons not to. In reality many people also wouldn’t just because they consider it creepy or wrong.
The other point is, I suppose we are giving back when we are buried because we return to the earth anyway. So to me, eating of the dead of your species is no different to that.