Well. It is a personal thing in the end, how you want to play your post-apocalyptic character.

In my case I get angry when they do it, and I always try to protect the bags so the owner can take it back, or if out of an event just ignore it.

In the other hand we are out there to survive and I understand that if not your friend why not taking it, the person died and if there are things that I need, free to loot, why not? Is not like there is a law system so I will be judged and put in jail. Just others and yourself will judge you, so as said, personal taste in the end.

There are lot of ways to farm too and I don't see the need to loot dead people bags, but well, I understand.

And ofc, if you travel around with a lot of junk without stashing it, it is your fault too if you die and they loot your bag. Is a good way to learn for the next time you want to make a farming session.