I disagree to the maximum extent possible. I have lived in 6 countries. Americans to me are by far most friendly and supportive of new ideas.

When you are visiting a place, you see it with rosy eyes. You are not forced to deal with the day to day difficulties of life, the commute, the commitments, the finances, the outrage about politics and so on. So, comparing the harsh reality of 'back home' against an environment where you don't have to deal with those is going to obviously come out different. When you live in a country for a while, only then the so-called 'bitterness' catches up to you.