You may be running non-free programs

http://www.gnu.org/philosophy/javascript-trap.html

So it's OK if the non-free code doesn't run in your machine?

So, plain HTML pages served by ISS are OK?

What about internet search providers?

What about... say... a remote terminal session?

Would these... people be happy with a dumb terminal, with all the proprietary evil code running away from them, just offering them the services but no code to run locally?

Be very careful about what you wish for.