Isolationism, "Europe's problem, no way that'll get to us"...haven't we as Americans learned that lesson twice? More?
And those 'complicated alliances' have thus far kept us out of WWIII, through all the nastiness of the Cold War and beyond. Why is Russia pissed at the idea of the Swedes and Finns joining NATO? They lose their ability to threaten and bully their neighbor, and walk right in when they don't get their way. Alliances are not perfect, Germany's obscene 'elephant walk' of Eurofighters where they had to tow a good portion onto the runway to stage the photo because they were all NMC is emblematic of the problem...but that doesn't mean you don't adjust or fix those things, and not junk the whole thing altogether.
And I'd say security is worth paying for, unless you like Novorossiya. And opposing that (a new Russian Empire) is a pretty fucking clear objective.