I'm sorry about that incident...
One thing that helps in coordinating a paceline while riding on a street with a not-so-broad shoulder and some traffic is to keep the lead changes to a minimum until there is less traffic/a broader shoulder but, if that is not feasible, to have the person who's dropping back do so from the right-hand side, i.e. on the outside of the road. Hence what the drivers coming from behind see is always ONE line of cyclist, and the lone cyclist dropping back is "protected" by the paceline.
I could imagine it would be harder for a car (and somewhat unexpected) to see a single cyclist against the background of the paceline...
I also agree that we should be polite, firm, but non-confrontational. I'm not too concerned with people carrying guns but then if I was in Florida I probably would be.
Good luck on your next ride...