Just a note that green card holders are residents, not citizens. They don’t get to vote, they just get to pay taxes.
Still potential for abuse of course, but an important distinction.
The difference between H1B and permanent resident is massive. Residents aren't beholden on their employer to remain in the country.
While there are time and other requirements after getting lawful permanent resident status (“green card”), the main limitation on access to citizenship is getting status in an immigrant category and thereby becoming an LPR.
PhDs on the other hand, regardless of the field, you've contributed something unique to the collective knowledge of humanity. Instant green card, it's even dumber to kick them out.
Green cards, also aren't citizenship but are simply a step to getting there. There are many types of visas that let you work but have stipulations, especially around leaving the country. If there really is some kind of fear of people collecting citizenship after spending decades in the country and becoming highly educated, special visas with rules are always an option. But there should be a viable path to citizenship either way. We should not be kicking these people out.
Depends on the field. I've met PhDs that are fantastic, and I've also met PhDs whose defining contribution to human knowledge over their entire lifetime was "I made this algorithm 2.3% faster in a specific tiny edge case that no one will ever care about."
That's pretty much what most research or even startups are like. You bet that 5% will blow up, and hence you fund the other 95%.
Seems like an interesting idea. Why do you think it's not already being done? I haven't really explored the idea very carefully, but this would amount to giving universities the power to grant citizenship to foreigners, which seems like it has a lot of potential for abuse.