Yes it's true that people shuffle in and out, but you're making it seem like a lead researcher on a project leaving suddenly would have no impact on the work. Often times yes, a project can fail if key personnel leave. Many labs are just a professor and one grad student who they had to work for years to get up to speed. Many times that grad student is the one person in the whole world who has the specialized knowledge they do. Such is the nature of researching at the bleeding edge of a field. If they were to suddenly leave it would have a noticeably negative impact on their research output, even if the best American student stepped into the role immediately.
That you fail to consider that possibility but you are very keen to claim "racist and just hate Americans" leads me to unfortunately quote the HN rules at you:
"Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith."
That you fail to consider that possibility but you are very keen to claim "racist and just hate Americans" leads me to unfortunately quote the HN rules at you: