JavaScript applications are the exception in my environment and they threaten to burst that shiny bubble.
Aside: I really think that the terms "open" and "closed" are imprecise and confusing, which is why I avoid them. With deterministic builds and free software I have a mapping from source to corresponding binary; so while the binary may not be directly editable (or "closed") it still is free software and I could edit the corresponding source to obtain a new binary. In my opinion the problem really is one of practical software freedom, which has never been achieved in a satisfying way for web applications.
The only problem from a free software perspective is that not every line of javascript in the universe is explicitly linkable to a GPL license in a static file, as one would find in, say, a C library. But in every other way (I would argue, in every way that really matters) javascript in the browser is either as free or more free than other languages in their respective environments.
Ok, technically you could but that would be insane. Even if you consider how much FOSS exists on servers, it's impossible to ever be certain what is running the logic of a site unless you can run it locally, which defeats the whole point of the web.
But arguments that javascript in particular is hostile to user freedom seem a bit overstated... and even Stallman doesn't suggest the answer is getting rid of it altogether. Although he does seem to believe that only running free javascript somehow makes it safe to run... which isn't true.
This looks like a strawman.
For a user of a service there is no difference between a service provider that uses free software and a service provider that uses proprietary software. Proprietary software primarily harms the user of that software --- and in this case it is the service provider, not the user with a browser.
There are different concerns to outsouring computing and/or communication to services, but these are not the same concerns that apply with the use of proprietary software.
JavaScript applications, however, do run on the user's machine and thus the usual concerns about running non-free software apply.
> [Stallman] does seem to believe that only running free javascript somehow makes it safe to run... which isn't true.
I haven't heard him argue that position. Free software obviously can be faulty and it can be unsafe to use.