The FBI arn't Nazis, and there was a huge propaganda drive amidst poverty etc. Can ordinary people be convinced something is of the greater good? Absolutely. But to do this requires an immense effort where the speaker resonates powerfully with those he is talking to, and it requires a huge belittling of the people involved. Hitler spent YEARS delivering his message through every single media made available to him. As more people get on board with the idea, it snowballs and others catch on. It's harder to convince smaller groups, in secret, to commit mass murder when they are still exposed to outside influence that does not share your views. Only because of how World War One ended for Germany, did it set the stage for World War Two and it's subsequent horrors (they made the Germans out to be victims, not the Jews).
"It worked for the Nazis" is not a valid argument by any stretch.
Gun control lobbyists don't continually need to set up shootings to enforce their points - that happens on its own. It's not some conspiracy, it is the outcome of having so many guns, so accessible. Sometimes people do nasty things simply because they can, but it doesn't always mean there are other factors at play. Maybe there is, but I wouldn't call SWAT/ HRT members a ruthless killing machine incapable of conscious thought for a mere gun control policy