Longer answer, which guy-who-looks-suspiciously-like-G-ennesis-P-Orridge didn't cover:
Operation Castle was a clusterfuck.
Look. I can't point at wikipedia pages. There's stuff that former computer salesmen can't scrape off the internet and vomit back at you. I grew up at the knee of these guys. Two of the satellites taken out by Starfish Prime were being tracked by my dad for the Air Force. It meant that his six-month idyll in Honolulu turned into two months followed by four months in Thule, Greenland. He told me the sky turned the color of green jello.
So... I guess I did point at a wikipedia page. Take a look at the "notes" column. What you need to know is that we had really shitty models of what thermonuclear detonation looked like. Wikipedia claims Castle Bravo was off by a factor of two. I've heard a factor of ten. Things did not go as expected. They reefed back on Castle Romeo and it was off by a factor of three. Bottom line? We went out to test things in the middle of goddamn nowhere and still killed fishermen and irradiated islands rendering them uninhabitable by accident. Scuttlebutt was that the Soviet Tsar Bomba test was also a gross miscalculation of yield. Fusion reactions went from theoretical to "holy shit what did we just do" in the space of months.
So launch that shit into space.
Everyone freaks out about the EMP. The real effects of setting of a nuclear detonation in space? Shit-tons of ionizing radiation that doesn't go away for years. USAF had a few birds up to sniff the radiation; they weren't expecting them all to frickin' conk it within hours. They certainly weren't expecting to cook off a substantial portion of all satellites in orbit. Formal condemnation at the UN and shit. Bad news.
So on the one hand, you can't test on the ground 'cuz you'll kill people. But on the other hand, you can't test in space because you'll end the space program. But on the third hand you have to do something because the Soviets are thinking of running the blockade.
It wasn't so much "fuck you that's why" as "oh fuck we have no idea what we're doing and if we don't figure it out we're all going to die."
I knew a few people who went out here. None of them liked it. Couple of those were made by my grandfather.