On it's own I think this switch is a bad idea because it's too big of a hammer. Someone shouldn't accidentally disable TLS verification in pip for instance because they wanted to disable TLS verification for some random tool that only hit internal TLS but which didn't have it's own off switch written into it. A lot of tools are written in Python and it's hard for a user to really know what the full extent of toggling this switch on their system will be, especially given that they may have no idea which other tools are incidentally written in python (pip is not a good example of this, but there are lots of tools that are written in Python but which the fact they are written in Python isn't important or maybe even obvious).

I think keyed by site is wrong too, again because the scope is wrong. Opting out of security at the Python level filters down into tons of random applications that the end user may or may not be aware is even written in Python.

Part of the benefit of the current "opt out" mechanism is that it feels a little dirty to opt in in that fashion, and it should because globally opting out is breaking the security expectations that any application has now with the latest versions of Python, and adding a "cleaner" way of doing this is essentially giving people a nicer footgun (in the long term).

Now, I recognize that there is legacy systems at play here that are going to be around for a long time and that who this proposal is really being aimed to helping. My question would be, why can't those downstreams simply carry this patch? The attached patch is relatively tiny so it shouldn't be a very large burden, the largest being documenting and making people aware that such a thing exists on that platform. If there's enough downstreams who would reasonably have a reason to apply said patch maybe an addendum (or a new PEP) can be added suggesting that downstreams should apply said patch.

The tl;dr of my opinion is that if it weren't for legacy systems, I don't think anyone would propose this feature, and given the security sensitive nature of it I think it's best to treat this feature as a quirk of those legacy systems rather than a fully supported API of Python.