If you are in a dangerous situation that you can walk away from, then walk away from that dangerous situation as soon as you can.
The deceased wasn't in a dangerous situation when he pulled out the can of pepper spray; he was in an argument. And he was in an argument that he stepped away from and then came back to with the can of pepper spray in his hand.
Approaching someone with a can of pepper spray is a provocation, something anybody with an IQ over room temperature understands. (Did he deserve to be senselessly killed for it? Of course not.)
Virginia Commonwealth University - Pepper Spray
DO carry pepper spray on your person
Pepper spray is effective, but only if you have it with you! Whether you are walking alone at night, jogging around the neighborhood, or going to and from your car in a parking lot, you always want to have your pepper spray in your hand and ready to use. As always, its better to have it and not need it than to need it and not have it.
I hope this has clarified what i mean when I say that if you are in a situation that could become dangerous, you need to have your pepper spray in your hand.
Realizing we don't have a video of the entire event, I believe your description is wrong. The man with the pepper spray walked away from the altercation, but right into an armed man looking to kill someone, who tried to grab his pepper spray.