It seems the focus has shifted from "what would you do" to "is a attack with a paintball gun justification for lethal force"
The scenario as I see it is you are walking in a city that has known gang violence, a car pulls up and the window rolls down, you may or may not see someone point something that looks like a gun at you, and then you hear noise of the gun firing and you feel impact/pain.
I think most would return fire based on this scenario
If the scenario was you see someone point what is obviously a paint ball gun at you and shoot you with it, then I think most would just get out of the area.
When looking at if a response is justified or not, the scenario you are reacting to is going to play a huge part in determining if the response was justified. Think about the various news stories about individuals being killed by cops when all they had was a airsoft gun. I also believe justified or not, if you shoot someone that was shooting a paintball gun at you there will be significant legal consequences and you will be crucified in the new media.
John K