Who cares if it allowed the US to prosper? Freedom of speech is not about economic output but a value system. This utilitarian moral relativism might make sense in China but it is not part of modern Western culture. It was a civilisational conquest and a difficult one to obtain.
Values are useful. I don’t mean economic prosperity, I mean that our value system has largely worked.
What value system? You still have legal slavery!
There's a credible case it's just a happy coincidence. The large single economy with, until recently, open immigration policy were possibly bigger factors.
The US has prospered in war. It is in fact still basically prospering through war.