Americans all have this attitude that theyre "on the hook" for everyone elses defence as if theyre the white knight defending the world against evil. Its more like the local mob tough guys who have been taking protection money for the last 40 years backed down when a rival gang finally decided to make a move
I'm American, and I don't have that view. So it's clearly not literally true.
So perhaps you mean that it's "mostly" true. Then I'd ask, what evidence do you have to support that? Is there some poll of public opinion you can refer to? That's something we could meaningfully discuss.
Actually, your view is true even if there exists even just one person with your view. In reality what matters is the distribution of views. Furthermore, what matters is the distribution of views by the decision makers because those will be divorced from public distribution and informed by other secret plans or information unknown to public. So in a sense, it doesn't matter whether he is right or you are.