> Random websites can't be entrusted to run javascript in a way that's not hostile to my interests.

I encourage you to consider that any website that runs arbitrary code on your computer _at all_ is hostile to your interests, by default. Websites today are becoming more programs than documents; rather than presenting you with a download dialog like you'd traditionally see with software, your browser is clicking "Download and Run" for you.

Cooper Quintin of the EFF had a Privacy Badger talk at LibrePlanet 2016 that emphasizes just how many third parties you are "trusting" when you visit a website.

https://media.libreplanet.org/u/libreplanet/m/ending-online-...

I spoke more generally:

https://media.libreplanet.org/u/libreplanet/collection/resto...