> You're specifically visiting their website. You are explicitly requesting whatever they're serving up.
It would be preferable if I could visit a website without having to trust them to run code on my computer.
In general, it's preferable to make things as little intrusive as possible.
> a program you downloaded is gasp executing code on YOUR computer
The same is true for programs people download too.
There is too much abusive code, both on the web and in other programs.
When I download a program I do it from a trusted source.
The program has the source code available and I (and everyone else) have the right to read and modify that code.
The web can't work like this because:
1. Websites are so many that I can't trust all of them.
2. Even if the javascript is readable, it is tied to the rest of the website and can change at any time so any modifications or rewrites will stop working.