U.S. can't afford $18 billion of non-essential spending. It can't afford $1 billion of non-essential spending. In fact, it can't afford $1 of non-essential spending.
The argument "we're $35 trillion in debt so it's not a big deal to add 0.01% to it" is just incomprehensible to me.
And it's not just UN. It's $47 billion to USAID, $9 billion to NPR, $10 billion to California's "never gonna happen" rail, $1.3 billion to Harvard and that's just a small part of spending.
US government still needs to go on a serious spending diet. But every cut gets people to catastrophize how the world will end if US doesn't fund UN or Harvard.