The world works best when America leads.

– The late US diplomat Richard Holbrooke

One night, when I was editor of a news wire service on the graveyard shift in downtown Los Angeles, a respectable, middle-aged man in a neat business suit, calling himself Mr Wilson, approached me with a strange tale. We overnighters on duty alone at United Press through the long hours were used to being accosted by drunks, dopers, homeless people and a taster's menu of southern California lonely souls with their story. Mr Wilson, cleanshaven and persuasively reasonable, told me he'd just been kidnapped by aliens from Venus, had sex with their Queen ("the best of my life"), and then been safely deposited on Venice beach next to Santa Monica.

He was so plausibly likeable that I was almost convinced. So I drove him out to the ocean where, indeed, he was able to point out undeniable scorch marks in the sand where the Venutian ship had blasted off, plus three deep indentations where the tripod-shaped landing-gear of space vehicle had stood. Right then and there, I thought it possible I'd had my first encounter, if at second hand, with a real UFO.

I felt the same way when listening to Barack Obama's 28 March speech about his reasons for invading Libya on behalf of the anti-Gaddafi "rebels". For just a moment there he had me. "Some nations may be able to turn a blind eye to atrocities in other countries. The United States of America is different," he told the nation. In that UFO moment, a part of me wanted to believe that high-penetration US Tomahawks, which by some accounts are coated with extremely radioactive DU (depleted uranium), would be killing bad Libyans to save good Libyans and that our flying torpedoes would know the difference.

A significant section of what passes for the American left seems to share my fleeting suspension of ethics and political memory – by backing Obama's war against the third Muslim nation that did not attack us. This is the first war he did not inherit from George Bush (although he's done his best to make Afghanistan all his own). He has shown exemplary courage in facing down a fourth-rate tyrant with a fourth-world army with a toughness he has never shown against out-of-control Republicans at home. If you're afraid of the big bully in your own block, it's smarter to find a smaller one to fight over yonder.

Liberal hawks never seem to learn that you can't get healthcare, decent schools and less unemployment by bombing smaller nations. Military adventures trump domestic rehab every time. We Americans have a very long history – going back to Teddy Roosevelt in Cuba and Woodrow Wilson in the first world war – of progressives going to war for the best, most irreproachable, humane, idealistic reasons, whether that meant saving Belgian babies from fiendish Hun bayonets or rescuing Benghazi civilians today.

It's extraordinary to watch progressives like NBC's Rachel Maddow, the New Republic's John Judis, Kevin Drum of Mother Jones, Juan Cole and many others cheerlead the "Obama doctrine" of humane intervention – that is, meddling militarily at "low cost", usually ending in disaster for all concerned. Such liberal war hawks have serious records of fighting for good domestic causes. But what a disconnect!

You have to sleepwalk, or be in serious denial, not to grasp the blood-link between union-busting in Madison, Wisconsin and bunker-busting in Tripoli, Libya. It's not subtle. We are no longer an infinitely rich country. Our bridges, dams, pipelines and roads are falling apart. Our people are on food stamps and can't find work. Spilling our money on the desert renders it positively reasonable to cut, slash and degrade – that useful military euphemism – help for the poor and middle class. Obama's $75bn foreclosure prevention programme is a bungle due to "lax oversight": translated, that means there's been too much sucking up the mortgage-holding big banks that evict homeowners often illegally. And Obama takes this very moment in our rising-poverty-so-let's-go-to-war crisis to cruelly, mindlessly, cut $3bn from LIHEAP, the federal government's energy assistance (heating oil and air conditioning) to the poor.

The arithmetic is brutal. Each Tomahawk cruise missile fired from a sub, ship or land costs roughly $1m, and we've probably shot over 200 of them onto Libya, killing Gaddafi's military, paramilitary, civilians, hospital patients and – now we learn – our guys, the rebels, too. That's a $200m bill, straight off. The Centre for Strategic and Budgetary Assessments estimates that the Libyan operation costs the US between $100m and $300m per week, so we're heading toward the $1bn mark even if, as advertised, we pull back marginally. Let the jobless or disabled poor freeze their asses off this and next winter.

We on the left often accuse our ideological adversaries of "triumphalism" – a know-nothing superstition that America is and always will be "different", superior to all other nations, creeds and peoples. If we do it, it's right and moral because, well, we're Americans and we mean terribly well.

And if you believe that, I have a UFO I want to sell you.