Walmart manager shot after argument over service dog

This is really strange because if you look at the People of Walmart site you see folks in these stores with monkeys, goats, pigs, snakes, you name it and they are not escorted out so I don't understand why a dog would be a problem.

a service dog is one that licks you instead of himself and the owner had no capability to retrain it.

This person did more to harm the integrity and reputation of any service dog program existing! People who are involved in training, teaching, and owning service dogs are supposed to be screened to the nth degree to prevent this type of abuse. Service dogs are worth a LOT of money and should be off leash only at specific times and entering a store isn't one of those times! This owner was definitely abusing a privilege, if he even had one, but unfortunately it will impact on all those who depend on service dogs just to get through their daily activities. Apparently it's the owner who should be in a kennel!

Whats a service dog ? And why is it unleashed in Walmart?