You don't have to travel far on the Internet (or in the South) to find people defending the Second Amendment because it protects us from government tyranny. The basic idea is that, at some point in the perpetually imminent future, millions of Real Americans (TM) from across the nation will surge forth with their M16s and John Wayne commemorative six-shooters to take back this country from the twin demons of BIG BROTHER and YOUNG PEOPLE.
Faith in the ability of American gun owners to fight back against government tyranny is often expressed through image macros.
Thermopylae comes up a lot for two reasons: 1) Xerxes asked the Spartans to give up their weapons, and 2) Zack Snyder's 300 gives members of the "patriot" movement hard-ons that could burst a carbon-fiber condom. I've made a habit of correcting these macros whenever possible: