Well, I'm only a casual observer of the US's gun culture so this is something I could easily have missed. Could you post an example of some notable organisation or group that is calling for a complete ban on all private ownership of firearms in the US?
To me that seems like a very extreme position. Off the top of my head I can't think of any country where all private ownership of firearms is forbidden, and a quick look on Wikipedia comes up with only 11 countries where that is the case, and most of those are small island nations.
Which isn't to say that I don't believe that it may be the case. There are, after all, plenty of examples of groups or organisations who do advocate for extreme positions. But it is one that I don't remember seeing espoused by any group in the US, so would definitely appreciate being pointed in the direction of one.
Opinions don't only exist (nor cease to matter) only when one can point to an organized group that holds it.