It's the fault of the thieves for making the decision to steal in the first place. Even if I were a LEO I wouldn't shoot someone for shoplifting, but if I stole something from a store, I would definitely expect that someone else (security guard, clerk, LEO, bystander) would shoot at me. I tend to assume others are less conscious of liability and less forgiving than I am, and thus more willing to shoot.
In almost any situation, there are correct choices and there are easy choices. The correct choice would have been to go to a social services organization, appeal to a church, etc. The easy choice is to shoplift.