A common statement from the fans of government monopoly on force is: “no civilian needs such weapons”, with “such weapons” being whatever they are trying to ban. Let’s look at this statement more closely.
The Secret Service staff are civilians. Police officers are civilians. All government organizations other than the five branches of the military are civilians. Secret Service agents have access to submachine guns like the P90 above, as well as much more powerful weapons. Why? Such arms are useful in protecting lives of the people they are trying to keep alive. Quite a few regular Americans — such as stalking victims — face daily risks at least as severe as those faced by the political elite.
So we have plenty of examples of civilian government employees using modern guns unavailable to the rest of the population to protect themselves. In addition to government employees, corporations (“special occupational taxpayers”) can own guns denied to the general public. These corporations are definitely civilian structures, yet they own all kinds of high-tech weaponry far exceeding mere small arms in scope. Apparently, lots of civilians have a use for modern guns. Why shouldn’t lawful individuals be able to exercise their rights the same way?