Possibly none, as long we don't construct an immigration system under the assumption it's a crisis that there aren't enough PhD graduates in STEM fields, and do

Possibly none, as long we don't construct an immigration system under the assumption it's a crisis that there aren't enough PhD graduates in STEM fields, and don't claim this "crisis" is a good reason to restrict people's immigration rights through force of law based on whether they complete a PhD in a government-approved field. If the market's answer is "don't do a PhD", that's fine by me. The problem is when people who want to hire STEM PhDs don't like the answer and have the government ask again on their behalf.