I am a green card holder in the USA in a mathematics academic career. Recently, in a discussion, I criticized various aspects of the USA, especially its politics. A citizen rebutted with "If you don't like it here, why are you here?" (Implicitly saying: "As an expat, you don't have a right to criticize the USA's politics.")
The possible responses that came to mind were the following.
In spite of its problems it is still a good place for a STEM academic career and having a green card makes it easier to travel across the world for academic work.
There are other immigrant-friendly countries which are good for a STEM academic career, however Canada is too cold and Australia/New Zealand are too far from anywhere!
The USA needs people like me and so the opinions of people like me do matter at least a bit. If the society/state here becomes too unattractive for people like, it will be the USA's loss.
The USA is largely populated by (willing or unwilling) immigrants.
Since the question was asked somewhat aggressively and none of the above answers appeared adequate/appropriate, I did not actually respond.
This question is primarily addressed to those who are expatriates in the USA, but others please feel free to respond as well.
Q1: How would you respond to this question?
This related/secondary question is primarily addressed to those who are in STEM academic careers, but others please feel free to respond as well.
Q2: Do you think that other countries are becoming more attractive for people in STEM academic careers?