That photo has made a lot of rounds, I figured it was photoshopped.
I also have to give great credit to the artist that did so, it was brilliant. Certainly the original miscreant got embarassed.
Personally, while DW might have done some things differently in handling the dangerous felon, when he first came upon him he only tried to get them to move out of the street. It wasn't until the encounter began to unfold that he realized he had the robbery suspect on hand, and as a cop I would expect him to affect an arrest, not necessarily waiting for a battalion of the National Guard to arrive to back him up. He carries a gun to defend himself from violent felons if the need arises. This time, it rose.
MB was the actor who decided to commit a crime (robbery), to commit another crime (assault) to get away with the first. His actions resulted in his death. I don't fault the officer for firing at what was a clear threat, the officer does certainly not have a duty to retreat just because a person is violent - his job is to handle violent people and remove the dangerous from the streets for processing by the courts. He did his job, maybe not flawlessly, but well enough. MB has himself to blame for his demise.
*Pants Up, Don't Loot!*