They will always allow it as long as you have javascript or any other code.

How would they prevent it? If they allow your app to read a value client side, it can do whatever it wants with it, including sending it.

If your app needs to present different behavior based on user settings, it needs to read it.

They allow this because they are being developed to allow this.

Browsers that don't allow this in a Web-like system without such functionality (like Gemini) can be written in two days or a week if you don't hurry.

Or at least take as long as Mosaic or Arena took to become usable.

Enormous resources are being invested into continued development of a platform where users provide valuable feedback.

By the way, ML is long past the point where that data could even be interpreted ambiguously. Those who have the data know exactly who you are and probably some useful traits of what you are thinking the moment you are typing a comment at any big website.