Most (if not all) browsers allow you to disable JS, so that seems like the perfect preference for you. I know it works on Chrome and Firefox on desktop (I use the NoScript extension myself, that blocks JS by default but allows you to enable it per-site), I can imagine it works the same on smartphones as well.
I /think/ what they're asking for is a world where turning JS off is actually a real option. Currently the web essentially does not work in such a case, so while it technically exists the option to disable JS isn't actually an real option.
So what they want isn't the power to turn off JS in their own browser, but the power to turn it off in other people's browsers (at least the browsers of people developing websites).
More seriously, I guess they might want a way of avoiding sites that don't have a good no-script experience. Perhaps if there were a trustworthy way to vote on that (or detect it automatically), someone could offer an extension which puts scary red boxes around hyperlinks which point to such sites.
