Proprietary javascript is no less harmful than any other proprietary software. Read Richard Stallman's essay "The Javascript Trap" to learn more. Javascript, due to its ephemeral nature, makes it impractical to exercise your four software freedoms. For a good analysis of the problems with javascript, watch Mike Gerwitz's talk "Restore online freedom" delivered at LibrePlanet 2016.

These days, many sites break down completely and do not function at all if you will not execute their javascript. However, there are also sites like ebay, that can function in part without javascript, but refuse to cooperate and hinder the user by covering the page with a noscript mask that blocks the user from accessing anything on it. So, to get around the problem, I wrote a trivial (greasemonkey) user script to remove the noscript mask by setting its CSS display property to none.

var style = document.createElement("style");
style.innerHTML = "noscript { display: none; }";
document.body.appendChild(style);

You can get this user script on greasyfork.org, or right here at the following download link.