In a shtf situation, you do what you have to do to survive. Most people are going to abandon their homes in favor of greener pastures so why not pick up what I want or need if its just sitting there un-used.
Because there are worse things in this world than being shot? I've got two trucks right now that are un-used. Is it okay for someone to steal them? Moral relativism will get you dead. If you don't own it then it isn't yours. Pretty clear. Prepare for you and yours and the issue is moot.