“Being allied with Europe and helping them to defend themselves is in the US interest — but not if we have to carry them.”
Why should we defend countries that won’t defend themselves? All those mooching countries got the peace dividend, we didn’t. Our defense budgets never went down.
Arguably, if Europe is a bunch of dependents reliant on the US for their defense, we gain considerable leverage over them and can induce them to favor US interests. Yet the better arrangement obviously is that they pay their share of defense costs.