> The allies are derided for literally freeloading on US military protection while underinvesting in their own defense.

1. No one forced the US to spend a bajillion dollars on defense.

2. The US did so out of their own free will, and out of self-interest: their power hegemony allowed for peaceful trade routes that benefited the US economy and US corporations.

3. Their own defense against what? What threats, until fairly recently, did the Europeans face that they needed to spend money protecting against?