The Syrian people were armed, that turned out well.

Your AR-15 isn't much use against the Airforce's F15. The world has moved on since 1776, local militias can't cope against national military - even one as an expedition force, and in the U.S specifically entire countries can't cope against the U.S. military as an expidition force, what hope does a local militia have against a U.S. based military?

The most you'll get is a guerilla war and terrorism, and that always works out well./sarcasm

Then why hasn’t the mighty US military been able to defeat a bunch of Afghan rebels armed with AKs? You vastly underestimate the power of guerilla war. See also Vietnam, Iraq, and Syria.

And if the US military ever turned against its own citizens on US soil, you can bet a huge number would defect and hell would break loose.

Well if your end goal is to reduce your country to the state of Iraq or Syria, with suicide bombers and destruction of entire cities a daily occurance, that's fine, I guess it's the price you have to pay for having weekly school shootings.

You conspicuously missed the example of Vietnam.

This is the EU. They don't have "amendments".