Dismissing fact as opinion is no argument unless you are arguing the fundamental nature of knowledge and reality. Perhaps, there are no facts and instead widely held opinions?
However, when one argues rifles are just rifles, and assault is something done by a person and not an accurate description of a rifle, you cannot deny the design intent and purpose of the rifle. Bolt action and semiautomatic rifle technologies are designed with specific intents. One is designed to hunt one animal the other is designed to hunt many humans.
If self-protection is the concern, hand guns were designed to kill people and should suffice for personal protection unless of course you are confronted with an assault rifle or zombie apocalypse.