Pretty much any gun will work in most civilian encounters since just having one is usually enough of a deterrent that firing is not even necessary and if shots are fired, most criminals will cease hostilities and flee. Other than that, in situations where you have distance and will two hands on the gun, I think a single-action revolver will likely be adequate providing the owner is competent in it's use. However, most civilian self-defense encounters occur at at extremely close if not contact range.

My brother-in-law has several Ruger Blackhawks and RedHawks and my experience with single-action revolvers is limited to exposure to his. They are big, heavy guns that would be relatively very slow to bring into action during a reactive close-quarter defense scenarios compared with something like a J-Frame. One handed shooting is the norm in these situations as you are either using the other one for defense or as a leveraging arm or are moving dynamically.

I've not drilled any Force-on-Force with a SA and never will since I have no need or desire to, but I still think they would likely present some serious problems in the most likely encounters an armed civilian might find themselves in whereas the enclosed hammer snub revolver is nearly ideal for them.