I think it has a lot to do with the Cold War way of looking at things. A lot of Americans felt like we were protecting the world against the USSR. And I do think that military power was important during the Cold War. A big part of our strategy for defeating the Russians was to just keep on spending money and forcing them to compete because we knew their economy was weak and flawed and that making them spend money would hasten their downfall. It's a big reason why we got into the space race as much as we did (I think that it's legit a massive human and scientific achievement too). Plus, it was deterrence from them taking offensive actions against our allies and interests. This obviously led to a lot of bad decisions like Vietnam and many actions in Latin America. But it also greatly benefited South Korea (even with their problematic governments) and Europe.

Plus, you have the WWII thing where we fought the Nazis and Japanese. The world is a better place because they were defeated and because of our involvement.

Now, with the downfall of an aggressive rival superpower, I have no idea why we have any need to keep on spending like we do. It's totally unnecessary and a money pit IMO and there's a lot of jingoism that goes into it.

Frankly, outside of Boomers, the attitude is most common in the poorer parts of the US. You'll hear it a lot less in successful cities than you will in dying rural towns. It's weird like that. I personally rarely hear it outside of Olympic years.

I couldn't really find any quality of life figures for the post-war period other than GDP per capita with a quick google, so maybe my perception of the post-war economy in Europe is off. But, we did give Europe over $12.7 billion ($133b in modern dollars) just through the Marshall Plan. The post-war recovery in Europe was certainly staggering though.