Yeah, that's the hugest barrier, but I can't think of any other solution.
It's unacceptable for us to just trust web hosts to not give us nonfree
Javascript, and automatic detection of whether or not a script is free isn't
a solution either even if it does it well (what if the website uses free
Javascript, but includes malicious features figuring no one will notice?).
Websites just need to stop using so much Javascript.
Of course, when you have a Javascript file accepted, it should be accepted
for all websites by default for better convenience; if you accept jQuery on
site A, you probably accept it on all sites.