It's gone in the US, and in the Western World for the foreseeable future. The why’s are complicated. There's a ton of legal and political history, and it's not all bad. The truth is, the so-called “givers” haven't always treated the so-called “takers” like humans (and the meaning of those concepts has changed radically troughout time), and it sort reinforces the idea that people can't be trusted to treat people like people. It's human nature. If only someone besides humans would take charge...
SciFi in the 1950-70’s was different. I like it better than today's, in general (George RR Martin... his Song of Ice and Fire/ Game of Thrones series is a masterpiece [and HBO does a great adaptation], I wish he'd finish it already.)
But, The Moon is a Harsh Mistress, Starship Troopers, Stranger in a Strange Land, etc, are awesome. Written by a man who loved humanity and loved in country. By the way, same can be said for Slaughterhouse Five, Breakfast of Champions, and Cat Cradle, different people, different perspectives, but the same love of mankind in general and the American way in particular, but very different.
I'll finish “The Mote in God's Eye” tonight, which has some of that same militaristic honor vibe, and some cool human nature commentary. A great book.
Orson Scott Card wrote Ender’s Game for every kid who though they were smart but misunderstood. The other books in the Ender Quintet were Antrhobology 101 for Americans who though they could understand other people and other groups by applying their own views to explain the actions of others (another masterpiece, and I wish he'd write about whoever created that virus). Card has some beliefs that people who loved his work and his philosophy thought intolerant. they were surprised, and that shock made them mad. I think it's ironic given his message. As a SciFi writer, he's brilliant.
Also, read Patrick O’Brian. Not Sci Fi, at all, but a similar old school philosophy that won't be popular now, but was an awesome series.
But, in the end, I think this is simple. Until the late 1960’s, then changing through about 1980, our society started to reject the pre-196(4/5-ish) American culture, in favor of some Post-modern, more equitable beliefs, and that change included the arts, movies, literature, TV, etc. That wasn't all bad. There were major inequities and cultural failings in our country and Western culture that were ignored. The problem was that we started ignoring the good stuff that was there, and too many of today's people forget the good.
It's a shame. It's also probably a luxury of being rich and safe, or fat dumb and happy for too long.
Ah, yes; great idea. Keith Laumer explored it...
You might want to try out some of John Ringo's books. The first book in his Aldenata series is A Hymn Before Battle, and is available for free at Baen Publishing's website at the aforementioned link. The Last Centurian is not free, but you won't find a more conservative freeper-style book short of Matt Bracken.
You might also want to look at the work of Tom Kratman. He’s collaborated with John Ringo on a couple of books, and written some on his own. Also, Michael F. Flynn writes very intelligent, not left-leaning books. He’s been compared to Heinlein on numerous occasions.