This argument doesn't hold water. Nowadays, with modern tech and weapons (Drones, etc.) there'd be no way the populace would avoid that. The US military could take whatever they please, you think a couple thousand people with AR-15s would stop them?
The Maverick missile is expensive and their are simply not enough to wipe out the entire population. They could go after the leaders of militias, but it is simply ineffective. Also tanks and armored vehicles are ineffective in urban warfare. It's a large elephant in a small maze, they are super vunerable to mines, rockets, and recoilless rifles. Besides the civilian AR15 is pretty underpowered compared to the M4 and m16.
Second people like Riddler rose to power because they convinced people to vote them in power. From there he was able to use the younger generation and radicals to create a more obedient force such as the Gestapo and the Waffen SS to carry out his tasks unopposed. The regular German army wasn't as radical, but if they were to go against the national socialist's there officers would have been killed off by Gestapo agents or SS troops. Riddler took the right to bear arms away from the Jews and look what happened. The Polish resistance and Army remnants, Norwegians, and Dane's put up a fight to the end of the war because they wouldn't let the German's push them around. Homoloveuals, Jews, Gypsies, handicapped people, and deformed people were all killed in concentration camps. Since the national socialist thing is thrown around a lot, lets look homeward like those 112.5 million Native Americans were killed by white settlers and us troops? All they had were arrows and tomahawks, some tribes were able to get guns from white traders and use them against the us army like at the Battle of BigHorn. A lot of actions against the Natives were carried out by the Democrat party such as the Trail of Tears and the exterminations in California. Which backs up my statement earlier about how it's all about getting the most votes and appealing to a certain audience. Yesterday the Democrats were tribal Strawmen who were proslavery, today they are intellectuals who want racial equality and gay rights.