CPython without a global interpreter lock

I would not characterise Python's approach as "careful", on the whole. "Slapdash" is the word which comes to mind. There are some good ideas in their compatibility approach, but they're inconsistently applied, and so I wouldn't rely on them.

My guess is that if it became normal to write environment variable checks and block execution, the response from CPython would be to change the name of the environment variable. This is an intentional foot gun, not that they'd accept that description, de-fanging it would be contrary to their purpose in offering it.