If I am armed I'm not going to allow anyone to pepper spray me and potentially take my weapon to be used against me. Pepper spray in and of itself may not be deadly, but it will incapacitate and render you defenseless, at which point the attacker can further harm or kill you. For this reason, being attacked with pepper spray can put you in reasonable fear for your life and safety and that would make lethal force an appropriate response in at least some cases.
That said, if I go armed to a protest where I plan to physically confront others and pick a fight, when I am successful at doing so and get a face full of hot sauce, it's hard to say shooting back was in self-defense. That's right up there with robbing a store and gunpoint, and when the clerk pulls a gun to fight back, saying you shot them in self-defense. You have no real right to self-defense if you caused the fight.
I'm not saying it's impossible, just very hard. We should all agree that no amount of words or shouting or arguing should ever justify any kind of violence against another, even with only a can of (supposedly) less than lethal pepper spray. If you keep screaming into someone's face trying to get a response, don't be surprised if you are successful and get attacked. It doesn't make the initial attack any less wrong, or make you defending yourself with lethal force automatically okay.
And Stand Your Ground only applies if you are attacked in your home, or in some states if you are attacked in your car. You have at least a moral obligation, and in many states a legal obligation, to do everything you reasonably can to avoid a fight before you resort to using deadly force in self-defense. It's really hard to say you were in genuine fear for your life when you sought out the other side, actively engaged in a confrontation with them, then escalated it until you got a response you felt made using a gun okay.