IME, 9 times out of 10, web developers are using JS for non-necessary reasons. The user configurable settings of popular browsers make it easy to designate the small number of sites that actually require JS and keep JS disabled for all other sites. They anticipate that the user will not have one default JS policy for all websites. In other words, these web browsers do not expect that all users should just leave JS enabled/disabled for every website, they acknowledge there will be situations where it should be disabled.
However as we all know most users probably never change settings. Doubtful it is a coincidence that all these browsers have JS enabled by default.
The number of pages I visit that actually require JS for me to retrieve the content is so small that I can use a client that does not contain a JS interpreter. Warnings and such one finds on web pages informing users that "Javascript is required" are usually false IME. I can still retrieve the content with the use of an HTTP request and no JS.
There is nothing inherently wrong with the use of JS. It is nice to have a built-in interpreter in a web browser for certain uses. For example, it makes web-based commerce much easier. However, I believe the largest use of JS today is to support the internet ad industry. Without having automatic execution of code by the browser without user review, approval or even interaction, I do not believe the internet ad "industry" would exist as we know it.
I believe this not because I think having a JS or other interpreter is technically necessary, but because these companies have become wholly reliant upon it.
That's why disabling JS stopsa remarkable amount of ads and tracking.