One of the biggest things, and I didn't even realize this was a thing until recent comments online, people around me, and other media outlets, is that some people are legitimately scared that the government is turning against the American people. That Barack Obama is either a Muslim (not that there is anything in the slightest wrong with this), the Anti-Christ, Hitler, or a combination of the three.
People are using this adhere to the Second Amendment of needing to protect themselves from the inevitable government oppression that is turning America into 1930's Germany.
When you use a straw man future argument for securing "liberties" it becomes extremely difficult to have a rational and useful conversation on anything.
This applies to guns, Muslims in America, the Second Amendment, and many other things.